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Senate 2020: The Primary Challengers


— The postwar renomination rate for Senate incumbents is 96%. That’s a little bit lower than the rate in the House.

— However, no senators have lost renomination in 13 of the last 19 elections. So recent history does not necessarily suggest that there will be even a single Senate primary loser.

— A few senators appear to face challenges that could threaten them.

— Primary upsets could change the general election odds in some key races.

Map 1: Senate seats contested in 2020

The Senate primary calculus

The last time this current crop of senators, Class II, was up for election, in 2014, no senators lost their primaries. This represented a change from the previous two cycles, which featured significant primary upheaval, particularly on the Republican side.

In 2010, three incumbent senators lost renomination in races all featuring odd circumstances: Sen. Robert Bennett (R-UT) may have won an actual primary, but he finished third at a party nominating convention, meaning he didn’t get to advance to a primary. Sen. Arlen Specter (D-PA) feared a GOP primary, so he switched parties, but then he lost in the Democratic primary; Sen. Lisa Murkowski (R-AK) lost the Republican primary, but then prevailed as a write-in candidate in the general election. Two years later, Sen. Richard Lugar (R-IN) lost his primary, which allowed Democrats to capture the seat.

An anti-incumbent sentiment on the Republican side contributed to some soft results for incumbents in 2014, but every challenger came up short. Still, Sen. Thad Cochran (R-MS) only narrowly survived a primary runoff, and several other Republicans turned in underwhelming performances. Sens. Pat Roberts (R-KS) and Lamar Alexander (R-TN) won less than 50% of the vote, and Sens. Lindsey Graham (R-SC) and John Cornyn (R-TX) won less than 60% (none of these incumbents faced strong challengers and all benefited to at least some degree from splintered opposition). Sen. Mitch McConnell (R-KY), then the Senate minority leader and now the majority leader, had to work hard to defeat outsider businessman Matt Bevin, although McConnell would win going away, 60%-35% (Bevin is now governor of Kentucky and he and McConnell have made amends). An appointed Democrat, Sen. Brian Schatz of Hawaii, also had a very tough primary.

Still, all the incumbents won that year, and in 2016 and 2018 as well. Every senator winning renomination in a given year has become fairly common: in 13 of the last 19 federal election cycles, no Senate incumbents have lost renomination.

A couple of weeks ago, we looked at the primary picture in the House. House members hardly ever lose primaries — incumbents who run have a better than 98% winning percentage in the post-World War II era — but usually there are at least a few members who lose primaries in any given year.

The topline victory percentages for incumbent U.S. senators seeking renomination are almost as lofty. Since the end of World War II, about 96% of Senate incumbents who have sought to be nominated have won renomination. The year-by-year history is shown in Table 1:

Table 1: Postwar Senate renomination rates

SourcesVital Statistics on CongressCrystal Ball research

Technically, an incumbent senator did lose renomination recently, albeit in an irregularly-scheduled special election that is not included in these overall statistics: appointed Sen. Luther Strange (R-AL), who lost to former Alabama Supreme Court Chief Justice Roy Moore (R) in a 2017 special election primary runoff. Moore would go on to lose to now-Sen. Doug Jones (D-AL) in the special general election.

Republicans currently have 19 incumbents running for renomination and reelection, while Democrats have only 11. So far, there is some primary action on both sides.

Let’s start on the Democratic side, where Jones faces a challenge. Earlier this year, state Rep. John Rogers (D) made some incendiary comments on abortion that drew the ire of many, including Jones (Rogers later got in a back and forth with Donald Trump Jr. and said the president’s son should have been aborted). Rogers also said he would challenge Jones in a primary. Rogers has yet to file with the Federal Election Commission but has suggested that he has received a half a million dollars in campaign pledges (whether this is truly the case remains a mystery). So it’s hard to know how serious of a challenger Rogers is, but it does represent another headache for Jones, who already faces an uphill battle to win a full term. Jones is white while Rogers is black; the primary will occur concurrently with the presidential primary on March 3, 2020, and the electorate will be majority African American. But Jones also really hasn’t done anything to draw the ire of Democratic primary voters, black or white.

Sen. Ed Markey (D-MA) may face the most significant challenge on the Democratic side at this point. Labor lawyer Shannon Liss-Riordan (D), who led a class-action lawsuit against rideshare giant Uber, is challenging Markey; so too might Steve Pemberton (D), a successful business executive who endured a difficult childhood in the state’s foster care system. Again, it’s not obvious Markey will be in trouble, although a recent Boston Globe/Suffolk University poll of the state’s presidential primary showed him at just 44% on a ballot test, somewhat weak for an incumbent (Liss-Riordan and Pemberton each had 5% support while 45% were undecided). An earlier poll, conducted late last year by UMass Amherst, showed Markey struggling in matchups with bigger-name potential opponents than the ones he has now. So there’s some softness there. The Massachusetts Senate primary won’t be until Sept. 15 of next year, while the presidential primary will be March 3, so there’s plenty of time for Markey’s opponents to try to chip away at him. The incumbent could benefit from facing split opposition, as there’s no runoff in Massachusetts.

Another Democrat who has a primary challenger is Sen. Dick Durbin (D-IL), who is being challenged by newly-elected state Rep. Anne Stava-Murray (D). Stava-Murray has been critical of state Democratic Party leadership, and she refused to support long-serving state House Speaker Mike Madigan (D).

If Sen. Tina Smith (D-MN) was going to face a tough primary, it probably would’ve been last cycle, when she was running as an appointee; she won the remainder of former Sen. Al Franken’s (D-MN) term last November and is running for a full term in her own right next year. Speaking of Franken, he is still sitting on a $2.6 million warchest and seems to be getting antsy to try to re-enter the political fray after his resignation over inappropriate behavior toward women, although there’s been no indication he’s seriously pondering a new campaign.

Finally, New Jersey law allows Sen. Cory Booker (D-NJ) to run concurrently for reelection and on the presidential ticket, although his presidential bid has not reached top-tier status thus far. Booker shouldn’t have much trouble getting renominated in any event if he does indeed run for Senate.

On the Republican side, it may have seemed at the dawn of Donald Trump’s presidency that the aforementioned Lindsey Graham (R-SC) would be in major primary trouble, given that many conservatives were already suspicious of him before he became a major Trump critic during his own run for the GOP nomination in the 2016 cycle. But something funny happened after Trump got elected: Graham turned into a devoted ally of the president and became the chief defender of embattled Supreme Court nominee Brett Kavanaugh during Kavanaugh’s ultimately successful confirmation battle last year. South Carolina Republicans have noticed and applauded Graham’s change: According to Winthrop University’s polling, Graham’s approval with Republicans and Republican leaners has risen 33 points in just a year, moving from just 41% in February 2018 to 74% in March. At this point Graham appears well-positioned for renomination.

A couple of 2014’s weaker performers, Sens. Pat Roberts (R-KS) and Lamar Alexander (R-TN), can’t lose primaries next year because they are retiring. Thad Cochran (R-MS) died two weeks ago after resigning due to poor health early last year; his replacement, Sen. Cindy Hyde-Smith (R-MS), won her special election primary and general election last year with the backing of President Trump, which she likely will be able to call on again if she has any credible challenges as she seeks a full term in 2020. Sen. John Cornyn (R-TX) and Senate Majority Leader Mitch McConnell (R-KY) both seem to be in fine shape. McConnell does have a challenger, former state Rep. C. Wesley Morgan (R), but the majority leader doesn’t face the kind of opposition from outside conservative groups that he did in 2014.

Probably the most significant Republican Senate primary challenger so far is businessman Garland Tucker (R), who is challenging Sen. Thom Tillis (R-NC). Tillis appeared to please no one earlier this year when he wrote an op-ed opposing the president’s emergency declaration at the southern border only to change his mind and vote against a subsequent Senate resolution disapproving of the declaration. After this piece initially posted, Politico reported Thursday morning that another potential Tillis challenger, Rep. Mark Walker (R, NC-6), decided against a challenge, which removed a potentially stronger Tillis opponent from the equation. Sen. Ben Sasse (R-NE), a sometimes Trump critic, also backed Trump on the declaration after expressing some skepticism about it, although it’s less clear whether he’ll face a real challenge.

Sen. Susan Collins (R-ME) probably helped shore up her right flank with her support of Kavanaugh’s confirmation last year, but she has a primary opponent, Maine Republican Party State Committee member Derek Levasseur. The other Republican running for reelection in a state won by Hillary Clinton in 2016, Sen. Cory Gardner (R-CO), has already endorsed Trump for reelection, perhaps as a way of warding off a primary challenge (no one credible seems to have emerged as of now).

Finally, appointed Sen. Martha McSally (R-AZ) does not yet appear to have a major primary challenger, but Senate appointees don’t have the same power of incumbency that normal incumbents do (ask Luther Strange), and Arizona Republicans can be a rambunctious group. McSally may or may not end up having a free pass to the general election.

One would think that a Trump endorsement would largely seal the deal for any of these GOP incumbents, although that ended up not being the case for Strange in 2017.

There is the possibility that some of these primaries could change the general election calculus: If Republican incumbents such as Collins, McSally, or Tillis were to lose a primary, it could hurt the party’s chances in the general election. The same is true for Jones — he’s the only Democrat who could hold the Alabama Senate seat, and even then he faces a difficult task.

Unlike in the House, where we can be reasonably confident at least one and probably more than one incumbent will lose his or her primary, the recent history suggests that we shouldn’t be surprised if every Senate incumbent wins renomination next year.

None of these Senate incumbents seem to be in obviously major trouble. That said, Markey (D-MA) and Tillis (R-NC) probably should be taking their primaries the most seriously at this early point.