What all of these vulnerable senators have in common is that their success depends on winning a fair share of relatively moderate voters who traditionally vote Democratic in presidential elections. All of the Republicans won in no small part by faring better than Republican presidential candidates usually do in socially moderate areas, like the suburbs around Philadelphia, Columbus, Ohio, and Chicago. Rob Portman, the Ohio senator up for re-election, won Columbus’ Franklin County by 3 percentage points, a county Obama would carry by 23 percentage points in 2012.
Big danger to Republicans
The fight over Scalia’s replacement could easily affect, or be affected by, the vulnerabilities of these senators. The debate would pose a big danger to Republicans who depend on winning moderate and socially liberal voters because it would elevate cultural issues — abortion, gay marriage or even the environment — where the party is generally on its weakest ground, especially in northern suburbs.
It’s impossible to know whether these considerations will be enough to persuade some of the vulnerable senators to support Obama, either in hopes of casting themselves as moderates or to insulate themselves from the culture war issues that might harm them in moderate areas.
Expect few surprises
Already, two of the five have come out against any Obama nominee. Ron Johnson, the Wisconsin senator, is one of the two. This is not especially surprising: He was the fifth-most conservative member of the Senate in the last congress, according to DW-Nominate, which scores members on their ideology based on their voting record. Johnson has trailed his Democratic opponent, the former senator Russ Feingold, in every survey that has been conducted so far this cycle.
Somewhat more surprising is Kelly Ayotte, a New Hampshire senator who has drawn a strong challenge from the state’s Democratic governor, Maggie Hassan. Ayotte has a less reliably conservative voting record than Johnson, but her growing national profile — she’s considered a plausible vice-presidential pick — might push her toward a more conservative stance.
Likeliest to support an Obama nominee
Mark Kirk, the Illinois senator, would seem to be likeliest to support an Obama nominee. He has the most moderate voting record and hails from a Democratic-leaning state — one that also happens to be Obama’s home state. The other two senators — Portman in Ohio and Pat Toomey in Pennsylvania — are in more conservative states and have more conservative records.
The Supreme Court appointment could prove to be one of the biggest issues in the presidential election if Republicans are able to block Obama’s nominee.
If Republicans succeed
Who gets to fill the Supreme Court, of course, is always an issue in presidential elections, and three justices are older than 77. But nothing would make the stakes higher than a vacancy that the next president would immediately get to fill. If Republicans succeed in blocking Obama’s appointment, it will make the party’s senators more vulnerable to the charge that they are obstructionists who are part of the problem in Washington.
The issue could still end up dogging those senators who choose to support Obama’s nominee, since a vote for them would still be a vote for the Republican-controlled Senate. It would naturally complement the Democratic message, especially if the Republicans nominate a divisive candidate like Ted Cruz or Donald Trump. That’s troubling for Republicans because there is a strong and perhaps growing tendency for close Senate contests to break uniformly in the direction of the party faring best nationally.
A political Catch-22
Democrats would be positioned to benefit in the Senate if the national race moved decidedly in their favor. They have strong recruits in another tier of less competitive states, like Indiana, Missouri and Arizona. The potential for extremism to cost Republicans in these states was amply demonstrated in the 2012 cycle, when Republicans lost races in Missouri and Indiana after nominating candidates who made controversial remarks about rape and abortion.
It’s hard to see a potential upside for the Republicans, considering the states in play and the view that the Democrats start at a slight disadvantage. The few Democratic states in play — Nevada and Colorado — are well known for social liberalism.
Whether these considerations are enough to sway Republican senators is an entirely different question. The policy stakes of replacing a conservative justice with a liberal one on a divided court are so high that it might still be rational for them to oppose Obama’s choice at all costs.
After all, if the Republicans lose the Senate and the presidency, the end result, a Democratic president choosing the next Supreme Court justice, would be the same as if they conceded.