It seems like eons ago that the 2010 Tea Party wave election eliminated the Democrats’ brief but highly destructive filibuster-proof 60-40 Senate majority of Barack Obama’s first term. Subsequent elections continued to erode the Democrat majority, with the GOP recapturing control of the Senate after the 2014 midterms.

But the six-year cycle of the Senate means that incumbents elected in Barack Obama’s first midterm election have to defend their seats in a presidential year, when turnout is generally higher. With a precarious 54-46 majority, Senate Republicans have the daunting task of defending 24 of the 34 seats at stake in this election, many of which they just flipped to GOP control in 2010. Thus, their margin of error is small.

Adding to the Republican headache is a highly controversial presidential candidate that several GOP contenders have backed away from openly supporting. “With just about any other candidate [than Donald Trump], we’d have been much better off,” opined GOP Sen. Jeff Flake of Arizona. Yet while some of these Republicans have constantly endured questions about their top-of-the-ticket nominee, the recent FBI revelations regarding Hillary Clinton may serve to tip the scales back toward the GOP — at least that’s a trend party leaders are hoping for.

Control of the Senate will hinge on a number of state races both sides believe can go either way: Florida, Indiana, Missouri, Nevada, New Hampshire, North Carolina and Pennsylvania seem to be the races to watch. As of the most recent polls, Hillary Clinton narrowly leads in Florida, North Carolina and Pennsylvania, but Donald Trump has stormed back to take the slim edge in New Hampshire, and he looks increasingly safe in Nevada to go with significant margins in Indiana and Missouri.

Of those seven races, four involve GOP senators who were first elected in the Tea Party wave: Marco Rubio in Florida, Roy Blunt in Missouri, Kelly Ayotte in New Hampshire, and Pat Toomey in Pennsylvania. Meanwhile, Indiana and Nevada are open seats that came about from retiring incumbents: Republican Dan Coats in Indiana and former Majority Leader Harry Reid in Nevada. Only Sen. Richard Burr of North Carolina (a two-term incumbent) defies this trend.

On the other hand, the GOP seems to be conceding defeat for two other one-term incumbents: Ron Johnson in Wisconsin appears destined to lose to the man he ousted in 2010, Russ Feingold, while Mark Kirk in Illinois labors in a state that hasn’t re-elected a Republican to the Senate since 1978, with only one Republican beside Kirk elected in that timeframe. (Republican Peter Fitzgerald defeated the ethically challenged Carol Moseley Braun in 1998; he served one term and chose not to seek another. His successor? Barack Obama, whose rise to prominence was made possible by a series of Chicago-style electoral dirty tricks.)

But while the GOP has to defend 24 seats, it appears at least 16 are going to safely stay in Republican control. With Democrats leading among senators not up for re-election 36 seats to 30 (and looking safe in nine of their 10 seats up for grabs, Reid’s Nevada seat being the exception), it means the GOP needs to win five of the seven races highlighted above to assure themselves control of the Senate — if they get four of the seven they will have to pray Trump roars back to snatch the crown from Clinton, because a 50-50 tie would mean the vice president is the tie-breaker (such as Dick Cheney was early in George W. Bush’s term).

And again looking at the latest polling in the various states, it’s most likely that Rubio, Ayotte and Blunt hold their seats while Rep. Joe Heck (also elected in the 2010 Tea Party wave) looks like the favorite to flip the Nevada seat. Conversely, Pat Toomey is in real trouble, while Indiana may return former Democrat Sen. Evan Bayh to the body — he chose not to run in 2010 and saw Coats, who he succeeded in 1998, return to the Senate. Bayh is battling Rep. Todd Young, yet another Tea Party wave winner who was elected to Congress six years ago. The former senator was the choice of Democrats to replace former Rep. Baron Hill (who Young defeated to enter Congress) after he suddenly withdrew from the Indiana Senate race in July after winning the Democrat primary in May. At the time Hill dropped his campaign, Young was heavily favored to win the seat, making Bayh’s entry “the textbook definition of a game-changer.”

Those polling results give the GOP a 50-49 edge, making North Carolina the decider — and polls have fluctuated wildly in that race. Burr has a slight edge overall, but well within the margin of error.

Given the trend of voters breaking late toward Donald Trump, next Tuesday may be a very late night to determine both the next inhabitant of the Oval Office and the status of the Senate. The fate of a bitterly divided nation may hang in the balance.