With Donald Trump dominating the headlines and cable-news shows, it's easy to get caught up in the machinations of the unfolding 2016 presidential campaign and lose sight of the stakes—which are even higher than a lot of people appreciate.
It's true that with Trump on the November ballot as either the Republican nominee (extremely unlikely) or as an independent (just plain unlikely), the dynamics of the race would be vastly changed. The only safe assumption at this point—that Republicans will hold on to their House majority, no matter what happens in the presidential and Senate elections—would be put in doubt as well. Anyone questioning that point should just look at Trump's unfavorable ratings among general-election voters, which are bad even among Republicans, or take a glance at polling on a three-way presidential election with Trump as the independent. A just-released ABC News / Washington Post survey showed Hillary Clinton beating former Florida Gov. Jeb Bush by six points head-to-head, 50 to 44 percent. But in a hypothetical three-way matchup, Clinton's lead balloons out to 16 points, 46 to 30 percent, with Trump pulling 20 percent and taking 14 points from Bush (and just four from Clinton).
Despite that caveat, I don't think Trump's name will be on the general-election ballot. That leaves us with four potential outcomes. In no particular order:
Scenario One: Good year for Democrats, as they hold the presidency and pick up the minimum of four Senate seats they need for a majority. Republicans keep the House, returning to the balance of power that existed before the 2014 midterms.
Scenario Two: Republican sweep, with the GOP picking up the White House while holding its Senate and House majorities. Even so, given the tough reelection races faced by many Senate Republicans, it's a decent bet the party will still have lost a seat or two, leaving the GOP a narrow but nowhere near filibuster-proof majority.
Scenario Three: A split decision with Democrats keeping the White House and Republicans holding their edges in the House and Senate—basically what we have today, but with a slightly smaller GOP majority in the Senate.
Scenario Four: A different split decision, with Republicans winning the presidency and holding the House but Democrats capturing a majority in the Senate.
To a degree, the presidential and congressional outcomes are linked—which makes Scenario Four fairly unlikely. I don't believe in coattails, but common dynamics can drive common outcomes: If there is an issue agenda, a political environment, and a particular set of voter-turnout dynamics working to elect a presidential candidate in 2016, those same factors will likely be at work in the most competitive Senate races. That doesn't mean the party winning the presidency will necessarily win a Senate majority, but with Republicans defending seven seats in states won by Obama in 2012, it is more likely than not.
The handful of Senate races most likely to be settled by a narrow margin—Marco Rubio's open Republican seat in Florida, Harry Reid's open Democratic seat in Nevada, and incumbent Republican Rob Portman's seat in Ohio—are also in states where the presidential race is likely to be close. A whiff of a breeze in any one of these states could easily tip both presidential and senatorial races in the same direction. Three other senators—Democrat Michael Bennet in Colorado, the only remotely endangered Democratic incumbent, along with Republican incumbents Kelly Ayotte in New Hampshire and Richard Burr in North Carolina—have no strong challengers yet, so each of these races is highly provisional. (Democrats are biting their nails to hear whether Gov. Maggie Hassan will jump in against Ayotte in New Hampshire.) But in all three, a strong wind for either party could have a domino effect.
And if Hillary Clinton—presuming she's the Democratic nominee—is running especially well, and her Republican opponent is foundering, it could bode ill for Republican incumbents Ron Johnson in Wisconsin, Pat Toomey in Pennsylvania, and Mark Kirk in Illinois, a state that President Obama carried by 17 points in 2012. Kirk's reelection fight is already uphill; the last thing he needs is an even stronger-than-expected headwind in a Democratic state that happens to be Clinton's birthplace. Some say that Johnson's race in Wisconsin against former Democratic Sen. Russ Feingold is uphill, while others simply say it's extremely competitive—but a weak top of the ticket is the last thing he needs as well. And while Toomey has done an extraordinarily good job of shoring himself up in a Democratic-leaning state, and has thus far been able to keep a strong challenger out of the race, it wouldn't take too good a year for Democrats to pull him down, even with a candidate who wouldn't normally be able to prevail.
Reviewing the possibilities provides an important reminder: These races do not occur in isolation. In an era of increased straight-ticket voting, the outcomes can be even more explosive one way or the other than they used to be.