The basic math of the 2018 Senate elections shows a challenge for Democrats. In order to win control of the upper chamber, the party need to successfully defend all 26 of its seats up for election (some of which are in highly red states like Missouri, Indiana, North Dakota, West Virginia, and Montana) while taking the open seat in Arizona and unseating Dean Heller in Nevada.* If Republicans manage to beat Democrats in just one of those races, then either Tennessee or Texas (both of which are very red) will likely become a must-win. If Republicans manage to beat Democrats in two or more of those races, then they’re very likely to keep control of the Senate.

And if the new results from a Morning Consult poll hold, the GOP’s path might become easier.



The key point in this graphic is Montana senator Jon Tester.

Tester has suffered a significant drop in his net approval rating since the last quarter (from positive 20 to positive seven), more than any other Democrat who is running for re-election to the senate in 2018. Each point in the graphic represents a Democratic senator running for re-election in 2018, Trump’s margin of victory (or loss) in his or her state (Trump won by larger margins in states further to the right and lost the states further to the left) and how much the senators net approval (approval minus disapproval) changed since Morning Consult’s third-quarter polls. Tester sits in the lower right hand corner—a red state Democrat whose approval rating has dropped.

This is just one poll—some of the movement in Tester’s numbers might be noise, and there’s more than enough time for any senator to change their numbers. But some of the movement might be due to his voting record.

Tester has benefited from taking some conservative positions and projecting a culturally conservative persona, but his voting record during the Trump administration may be causing problems for him. According to FiveThirtyEight’s Trump Score ( which measures how often a senator votes in line with the President), Tester sides with the president less frequently than other red state senate Democrats like Joe Manchin, Heidi Heitkamp, Joe Donnelly ,and Claire McCaskill. He has the lowest Trump-plus-minus in the upper chamber—meaning that he’s voted much less frequently than the partisanship of his state suggests he would. Moreover, Tester’s DW-NOMINATE score (a measure that assigns an ideological score to legislators based on which legislators tend to vote with each other) is currently to the left of Manchin’s, Heitkamp’s, Donnelly’s, and McCaskill’s scores.

Again it’s possible that Tester’s movement in the polls is due partially to noise or to state-level developments that I’ve missed. It’s also important not to draw strong conclusions from one poll or overlook some of the good numbers for Democrats (like Manchin’s and Heitkamp’s approval ratings). Also ideology isn’t a completely satisfactory answer here–Tester has survived staking out some liberal positions and taking some liberal votes in the past.

But whatever the right explanation is, it’s worth watching where his approval rating goes. It takes a strong Democrat to hold a state that voted for Trump by 20 points, and if Tester begins to show signs of weakness it could be a problem for Democrats

Tester isn’t the only senator who posted sub-par numbers in this poll. There’s good news for both the red and the blue team in the GOP numbers.



This graphic shows fourth-quarter approval ratings (vertical position) and the change in approval ratings since last quarter (horizontal position) for each senator whose seat is up for re-election in 2018 (color indicates Trump’s margin of loss or victory in each state in 2016).

There graphic shows two positive data points for the GOP.

First, Arizona senator Jeff Flake, ranked by Morning Consult as the second least popular member of the upper chamber, is neither polling well nor running for re-election. This isn’t news—Flake announced that he wouldn’t seek re-election months ago, and he polled poorly before that—but the poll is further evidence that if Arizona Republicans nominate a viable candidate ( they might not), Flake’s retirement will have ultimately increased the party’s chances of holding the upper chamber.

Second, Texas senator Ted Cruz has a 50 percent job approval rating. There’s not much nonpartisan public polling in this race, but a decent job approval rating for Cruz is a good sign for Republicans. Texas is a really red state, and Republicans are likely hoping that they can mostly ignore this race and focus on ousting Democratic incumbents in red states.

That being said, Nevada senator Dean Heller’s low approval rating is a good sign for Democrats. Heller is, as I’ve written previously, walking a tightrope. He needs to be Trump-y enough to fight off Danny Tarkanian, a primary challenger, while still crafting a message that might attract voters who preferred Hillary Clinton in 2016 ( Clinton won Nevada). If Heller is unable to differentiate himself from a generic Republican he may have trouble keeping his seat in the general election.

*Correction, January 25: This article originally said that the Democrats must defend 49 seats in the Senate in the 2018 election. That is the total number of Democrats in the Senate right now, but only 26 seats (including two held by independents who caucus with the Democrats) are up for re-election.