Good lord. It’s hard to out-eeyore the big A, but when I’m beat, I’m man enough to admit it. Well played, Sean Trende. Very well played.

He’s not saying it’s likely to happen, mind you, just that there’s a slim but not insignificant chance. His point is that, while it may seem like this year’s Senate races don’t matter — Obama will still be in the White House next year and Republicans will still control the House, so nothing’s getting passed either way — they matter a lot in determining who’ll control Congress when a new president’s inaugurated in 2017. The Democrats have a bunch of weak incumbents in purplish states up for reelection this year and they’ll have a bunch more in 2018. But in 2016 it’s Republicans who’ll be playing defense in Senate battlegrounds, an especially dangerous prospect given that turnout is always higher in a presidential election year and there are more registered Democratic voters nationally than Republican ones. As such, it’s highly likely that the GOP will lose seats in 2016, says Trende, just as it’s highly likely that they’ll win some this year. The money question is whether they can win enough in 2014 to ensure that they’ll still control the chamber after shedding a few seats two years from now.

How many constitutes “enough”? Well, after running several thousand simulations of the 2016 Senate elections, Trende finds it’s more likely than not that Democrats will win four seats that year. Which means, to give themselves a fair shot at holding the chamber into 2017, the GOP would need to win 10 seats this year, creating a temporary 55/45 advantage. Is that possible? Actually, yes — depending upon how dismal Obama’s job approval is this November. If it’s still stuck in the 40-43 percent range, a Democratic bloodbath on election day is a distinct possibility. And what if O’s job approval rebounds and the GOP performs much worse than expected? Then it’s … hard-liquor time:

The 2016 Senate landscape is so difficult for Republicans that, even if they win eight (eight!) seats this year and do well enough in 2016 to recapture the White House, Trende still thinks it’s more likely than not that the Dems will retake the Senate two years from now. Meanwhile, if the GOP underperforms this year and wins only, say, three seats, then not only is it virtually certain that Democrats will retake the Senate in 2016 but they’ll have a very outside chance of getting to 60 — a filibuster-proof majority,. How’s that for tonight’s nightmare fuel? President Hillary plus a Reid-led Senate that can rubber-stamp any Supreme Court nominee she wants. Dude, I’m nervous.

One big question, though: How likely is it that the filibuster will still exist in 2016, regardless of which party controls the Senate? If Democrats hold the chamber this year and a SCOTUS vacancy opens up next year, Reid will nuke a bit more of the filibuster and confirm the nominee with a simple majority. If the next president comes from the same party that controls the Senate in 2016, it’s a cinch that the majority leader will nuke the rest of the filibuster by eliminating the 60-vote threshold for cloture on legislation too. A “filibuster-proof majority” won’t matter soon; to the extent it does, it only means that Reid wouldn’t need to nuke the rest of the filibuster to pass Hillary’s agenda. But he’ll do it eventually, or the new GOP majority leader will. The reason to worry about Senate seats beyond the 51-vote threshold needed for control is, of course, because it gives you a margin for error. If Republicans end up with 51 next year, that’s nice, but no one thinks Collins, Murkowski, Kirk, and the rest of the RINO nucleus will hold the line against an Obama Supreme Court nominee. Fifty-one is important for keeping Democratic bills off the floor, but to make the majority RINO-proof, you need something in the mid-50s so you don’t have to worry about RINOs voting against you. Which is why even conservatives disgusted with the party leadership, especially on amnesty, will be sorely tempted to turn out this year.