FiveThirtyEight

Republican Sen. Jeff Flake of Arizona is unpopular — really unpopular. According to a poll about all 100 senators released Tuesday by Morning Consult, just 37 percent of registered voters in Arizona approve of their junior senator, compared with 45 percent who disapprove. That gives Flake a net approval rating of -8 percentage points, the worst of any senator. (Sen. John McCain, also of Arizona, and Senate Majority Leader Mitch McConnell of Kentucky both have higher disapproval ratings but better net approval ratings.)

Usually, polling numbers like that would be a big warning sign for a senator who is up for re-election in 2018, as Flake is. And yet, the Democratic field in the race doesn’t include anyone who has held elected office or a high government position (a common measure of candidate quality).

Democrats’ failure (at least so far) to field a strong candidate against Flake could hurt their already small chance of retaking the Senate in 2018. As I discussed Monday, the Senate map is very favorable for Republicans in 2018: Just eight Republican-held seats are up for re-election — out of the 52 they hold overall — and Democrats have to win at least three of them to regain a majority. Arizona looks like one of the best opportunities for Democrats to pick up a seat — if they can find someone willing to run.

On the surface, the reluctance to challenge Flake seems understandable. Beating an incumbent senator is a hard thing to do under even the best circumstances. And Arizona hasn’t been an easy place for Democrats to win in recent decades — the state has voted for the Republican candidate in every presidential election since 2000 and hasn’t elected a Democratic senator since 1988. Any Democrat running against Flake would face a scenario in which challengers have often struggled: Since 1982, senators who are members of the same party as the president and represent states that lean in the direction of the president’s party have a re-election rate of 85 percent in midterms.

But there is reason to think Democrats may have a chance in Arizona. The Morning Consult poll result is just one of several indicators that Flake’s re-election could, at a minimum, be in jeopardy. Let’s take a look:

1. Flake has pretty much never been popular.

The most recent Morning Consult poll is no fluke. The polling firm has consistently had Flake’s approval ratings at lower levels than those of many other senators. Other surveys have also generally found Flake to have a relatively low approval rating. Flake even commented on one of the surveys in 2013, saying: “Given the public’s dim view of Congress in general, that probably puts me somewhere just below pond scum.” There’s still time for Flake to recover, but the consistently negative view that Arizonans have had of Flake suggest that the feelings expressed in the Morning Consult poll won’t just blow over.

Flake is being squeezed from both sides of the aisle. Democrats voted heavily against Flake in 2012, and he’s done himself no favors with them by being a fairly reliable Republican vote this year. Some Republicans, meanwhile, are incensed over Flake’s continued criticism of President Trump. Flake would probably win most of those Republicans in a general election, but even a small erosion of his Republican support from 2012 could cause him to lose in 2018.

2. Flake barely won a first term.

Flake struggled at the ballot box in his one Senate race. During his 2012 bid for this open seat, Flake beat Democrat Richard Carmona by just 3 points. His showing was the worst for a Republican Senate candidate in Arizona since 1988. At the same time in the presidential contest, Republican Mitt Romney was coasting to a 9-point win over President Obama in Arizona. In other words, Flake underperformed the presidential lean of the state.

3. The 2016 results show a state shifting left.

Flake might not be able to win in 2018 if he underperforms the presidential lean of the state again. Trump won Arizona by just 3.5 points. That’s the worst finish for a Republican presidential candidate in the state since 1996, when President Clinton won.

Trump, of course, was hardly a typical Republican candidate, so his comparatively weak 2016 showing might not on its own suggest a leftward move for the state. Georgia’s traditionally Republican 6th Congressional District, for example, was more Democratic in 2016 than it had been in 2012; however, that did not foretell Democratic victory in the special congressional election there this year. But it wasn’t just Trump who last year underperformed previous Republican showings in Arizona. McCain won re-election by 13 points, which might sound like a wide margin but was a weak performance for McCain. He had won all his previous Senate races, dating back to 1986, by at least 20 points. And McCain wasn’t alone: In the state’s most populous county (Maricopa), the longtime and controversial sheriff, Joe Arpaio, and the longtime head elections official, Helen Purcell, were defeated.

4. There are other signs that Arizona may be moving left.

These shifts in state and local races may have been related to Trump’s unpopularity, but they may also be tied to a changing political environment. Throughout his presidency, Obama was less popular in Arizona than he was in the country overall, according to yearly data from Gallup. In 2012, for example, Obama’s net approval rating was 5 points lower in Arizona than it was in the U.S. overall. Later, however, Obama began to make inroads in Arizona: In 2016, his net approval rating there was only 1 point below his national net approval rating. At the same time, the state went from being 9 points more Republican than the nation in 2012 to 5 points more Republican in 2016, according to Gallup data on party identification. All of this suggests that the best way to describe Arizona is a Republican state that could go Democratic under the right circumstances — for example, in a year in which the Republican president has an approval rating nationally of less than 40 percent.

5. Flake needs to survive a primary.

Flake may not even make it to the general election. He’s being challenged in the Republican primary by the very conservative former state Sen. Kelli Ward. Other Republicans may join the race. In the 2016 GOP Senate primary, Ward lost to McCain by only 11 points, which was the closest Senate primary he has ever had. And Flake’s voting record in the Senate is ideologically similar to McCain’s. Additionally, the limited polling conducted late last year and early this year has shown Flake tied or trailing Ward. I’m not sure I believe those numbers, but it’s not difficult to imagine that Republican voters in Arizona, who went for Trump by nearly 20 points in the 2016 presidential primary, would be upset with Flake for his tendency to go after Trump.

If Flake were to go down in the primary, Democrats would be handed a golden opportunity. Open races are generally easier to win than those against incumbents. Also, Ward’s record is so conservative that any general election involving her and a viable Democratic opponent would probably start off as a tossup. Even if Flake doesn’t lose in a primary, he might be forced to shift to the right because of Ward’s challenge. That could make him more vulnerable in a general election.

CORRECTION (July 12, 9:45 a.m.): Because of an editing error, an earlier version of this story incorrectly said the U.S. Senate has 50 members. There are 100.