If the GOP nominates Donald Trump, it may well crater the party's chances of taking the White House in November. But it could have far broader effects than that. As The Week's Paul Waldman writes, nominating Trump makes a Democratic Senate in the fall a real possibility. And even the seemingly impervious House of Representatives is beginning to look vulnerable, according to the Cook Political Report, which recently shifted its rating of a number of races towards Democrats. Democrats are looking at the tantalizing prospect of unified government — though it remains a real long shot.

Six years ago, in 2010, we saw a Tea Party wave election. Many of those Tea Party-backed GOP senators are now up for re-election, which means Republicans are defending many more seats than Democrats. There are 24 Republican incumbents facing re-election in the Senate, versus only 10 Democrats. Republicans have a 54-46 majority, which means that Democrats need to flip five seats — or four, if there's a Democratic vice president to break a tie — to control the Senate. The Cook Political Report lists six Republican seats and one Democratic seat as toss-ups. It will be challenging for Democrats to flip the Senate, but hardly impossible.

The House is a different story. Republicans have a 30-seat majority; the Democrats would need some sort of GOP apocalypse to win the chamber back. But they might just have one in Trump. The Cook Political Report lists 14 Republican seats as toss-ups, versus only three Democratic seats. A pickup of 15 or so seats seems possible; 30, however, seems more than a stretch.

Still, given Trump-fueled Republican chaos, anything is possible. Here are a few potential outcomes, from least likely to most likely.

1. The GOP wins the White House, the Senate goes Democratic. This is not going to happen; if Trump or Ted Cruz overcome their standing in polls and somehow take the White House, it's going to be a bad, bad year for Democrats across the board. The chances of the Democrats winning the House while losing the presidency are even more remote.

2. Democrats win the House, Senate, and White House: This is a real long shot — Democrats would have to essentially sweep all contested House races. But if it comes to pass, unified control of the legislative branch would obviously make a Democratic president's job a lot easier. For the first time since the mid-1960s, Democrats would clearly control the legislative, executive, and judicial branches. (While Democrats controlled both houses of Congress in Obama's first two years, the Supreme Court still leaned conservative.) Hillary Clinton, who has campaigned in part as a pragmatist who could accomplish some of her goals in the teeth of Republican opposition, would instead face the unfamiliar prospect of actually being able to enact Democratic policies — a public health care option, a stimulus bill, higher taxes on the wealthy, the Sanders free college plan, and so on. Even immigration reform or gun control might be possible.

3. The GOP wins the White House and retains both the House and the Senate. You'd think unified GOP control of the executive and legislative branch would be really good for Republicans. Given the presidential candidates on deck, though, there's a non-negligible chance of intra-party backstabbing, recriminations, and general chaos. A continuation of the Republican primary season, in other words. This is one strong reason why the GOP might try to nominate a more mainstream Republican candidate at the convention: Marco Rubio, or Mitt Romney, or perhaps someone like Bill Frist. If they manage to do that, and then win unified control, they'll end up doing what the Democrats would do with unified control — passing a whole raft of conservative priorities. But if Trump or Cruz, both of whom are loathed by much of the GOP establishment, wins, all bets are off.

4. The GOP keeps the House and Senate, but Dems keep the White House: In this scenario, Democrats would probably still pick up a couple Senate seats. And that might give the Senate Republicans an incentive to be less obstructionist. As Jonathan Bernstein points out, the GOP is blocking the Garland nomination not so much out of ideology as out of senators' terror that they'll face a primary challenge from the right if they are seen as working with the White House. Primary paranoia is the main reason GOP senators won't even meet with Garland. They're afraid he'll give them compromise cooties.

If a few Republican senators lose in the general election, though, and if their losses are seen as being tied to the Garland nomination, suddenly intransigence may start to look like it has some downsides. A Senate in which Republicans are more paranoid about general elections than about primaries would be a much more functional Senate, even if Republicans remain in charge.

5. The GOP keeps the House, but Dems take the Senate and keep the White House: The Senate has already removed the minority's filibuster power for many appointments, and if Republicans continued to block a Democratic president's Supreme Court nominee, Democrats would surely remove the filibuster as an option for Supreme Court picks as well. It's likely Ruth Bader Ginsburg would retire before the 2020 election, and it's conceivable that Anthony Kennedy might as well. With the House in Republican control, there wouldn't be much hope for sweeping legislative advances, but the Democrats would plausibly have a chance to lock in control of the top court for a generation.

If Democrats take the Senate and the White House, it's also almost certain the House Republican majority will be smaller. Now, you might think that a smaller majority would mean more moderation — but there's reason to believe it won't. The House now has a few dozen very conservative members who are reluctant to vote with the GOP leadership on… well, on anything other than repealing ObamaCare, pretty much. And that was just enough holdout members to make it impossible for former Speaker John Boehner to pass legislation with Republican votes alone. Before he left the speakership, Boehner was forced to push through budget bills with Democratic votes. That strategy helped make him unpopular with his caucus, and led to his resignation.

Speaker Paul Ryan has so far avoided similar obstruction from his right flank, in part because Boehner pushed through a budget deal before he left. But when Ryan needs to increase the debt ceiling in March 2017, he may face a House GOP purged of members from purple districts like Rod Blum in IA-1 and Cresent Hardy in NV-4, and who have incentives to work with House leadership in order to appear reasonable and effective. The radicals, in other words, would hold an even greater balance of power in the caucus.