Republicans are feeling the best they have this cycle about their chances of holding their majority in the U.S. Senate, but doing that would require several states to break their way on election night. That's a risky place to be one day before control of the Senate is decided.

The tightening of the presidential race over the past week may have had an impact on these Senate contests. Most of the contests remain firm toss ups, though Democrats still have multiple paths to winning back the five seats they need (or just four if Democrat Hillary Clinton wins the presidency).

Illinois is all but assured of being in the Democrats' column, but it is the only seemingly sure thing. Former Democratic Sen. Russ Feingold's lead in Wisconsin has shrunk in the closing days and both parties are spending anew. Republicans, though, privately say they would be shocked if it broke their way.

The next two most likely to flip, Pennsylvania and New Hampshire, depend so much on the presidential race. Both are tight, but Democrats might have the edge because of a superior turnout operation. Weak GOP incumbents in Missouri and North Carolina continue to give Democrats an ever so slight edge, but in Missouri especially, the conservative lean of the state is certainly helping Republicans. North Carolina will also likely track closely to the presidential results in the battleground state.

Perhaps the biggest shift over the past week has been in Indiana. Former Democratic Sen. Evan Bayh hasn't had a cakewalk since he jumped into the race in July. His advantage here is gone, while Republicans are increasingly optimistic. And it's another state that's likely Republican in the presidential race.

Nevada, the lone GOP offensive opportunity, has sunk on the list of most likely to flip control with early voting in the state signaling heavy Democratic and Hispanic turnout.

Still, if Democrats do take back control of the Senate, it will be by a much slimmer margin than they had hoped for weeks earlier. And if it's a one-seat majority, get ready for another fight in a year if Clinton does become president. That's because Vice President Tim Kaine's Senate seat in Virginia will come open in 2017, and it would become the focus of a very competitive special election. Even if Republicans lose the majority, they would have every incentive to delay and not go along with major legislation. Why? The 2018 Senate map is a minefield for Democrats.

Expect some late calls across the board. And at least one race, possibly two, may go into overtime. The open Louisiana race won't be decided until a Dec. 10 runoff, because Tuesday is actually the all-party primary. And if Georgia GOP Sen. Johnny Isakson falls below 50 percent, he'll be forced into a Jan. 10 runoff. Both, however, won't decide the Senate, as they should stay in Republican hands.

Here's our final ranking of the vulnerable Senate races, from most to least likely to change party hands:

1. Illinois (R-Mark Kirk) Previous rank: 1

This one was baked a long time ago, and Kirk's downward spiral in the closing weeks certainly didn't help. No suspense here — Democrats start out at least a net one for the night with Rep. Tammy Duckworth poised to become the state's next senator.

2. Wisconsin (R-Ron Johnson) Previous rank: 2

It would be a pleasant surprise for Republicans if Johnson did hang on here in his rematch with former Democratic Rep. Russ Feingold. Final polling in the state showed this one was neck-and-neck, and spending from both sides has proven that. But Democrats view the last-minute investments as an insurance policy — you don't want to look back and regret not doing what it takes. If Johnson does pull what would be an upset here, it's going to be a very long night for Democrats.

3. Pennsylvania (R-Pat Toomey) Previous rank: 3

Clinton is favored in the Keystone State, but the margin may decide whether she takes Democratic nominee Katie McGinty with her. Toomey's pulled out all the final stops at the end, and his closing ad even quoted President Obama praising him for his work on gun-control legislation. But that tactic drew a sharp statement from the White House. Of the toss-up states though, Democrats feel best about this one while Republicans don't.

4. New Hampshire (R-Kelly Ayotte) Previous rank: 6

The Granite State is tight across the board, but when you factor in Democrats' get-out-the-vote operation, and the fact that late deciders typically break their way here, it might be good news for Democratic Gov. Maggie Hassan. Still, this one could go either way.

5. Missouri (R-Roy Blunt) Previous rank: 4

This race had to be a perfect storm for Democrats to even have a chance, and that's all happened. Blunt is viewed as the ultimate insider, and he hasn't taken his challenge from Secretary of State Jason Kander seriously enough. Kander, a war veteran, was an early, solid recruit. Still, the Republican lean of the state is showing up in polls. If Blunt is able to win, it will be Trump who carries him across the finish line — the opposite of most of the other races on here.

6. North Carolina (R-Richard Burr) Previous rank: 7

Burr has been another underwhelming incumbent, but former state Rep. Deborah Ross has taken plenty of hits from Republicans over her tenure as head of the state's ACLU. Burr's also had some foot-in-the-mouth moments that are adding to the GOP's headache here. As the presidential race goes, so likely goes this Tar Heel State contest, too.

7. Indiana (Open, R-Dan Coats is retiring) Previous rank: 5

No candidate has seen his stock fall as far and as fast as former Democratic Sen. Evan Bayh did this year. His late entry into the race this summer was heralded as a major shake-up, and it was, forcing Republicans to worry about this seat. But his double-digit lead has evaporated, thanks to questions about his residency, lobbyist ties and his final months in office back in 2010. Now, the momentum is all with GOP Rep. Todd Young, who has a slight edge in the final polls. Republicans are increasingly bullish, and with good reason. Trump's prospects have improved in the Hoosier State as well, which should help Young, too.

8. Nevada (Open, D-Harry Reid) Previous rank: 8

This is the only Democratic-held seat on this list. Republicans liked the trajectory of this race for months, but the state's Democratic tilt seems to have won out. An uptick in Hispanic turnout in the early vote, fueled by antipathy for Trump, isn't helping GOP Rep. Joe Heck, who has seesawed back and forth on his party's controversial presidential nominee. This state is hard to poll, but it almost always underestimates Democrats, particularly Latinos. Some Republicans point out that Sen. Dean Heller was able to win here in 2012 even as Obama carried the state, but his opponent, then-Rep. Shelley Berkley, was a poor candidate who was under a House ethics probe.

9. Florida (R-Marco Rubio) Previous rank: 9

There may be some Wednesday morning quarterbacking going on if Rubio is able to beat Democratic Rep. Patrick Murphy by just a few points. But caution: results may appear closer than they actually are. Some Democrats have begun finger pointing, saying they are missing a chance to take out a possible 2020 presidential candidate. But Democratic money was likely better spent putting multiple cheaper races into play. This is an incredibly expensive state, and the minute Rubio decided not to retire, he was going to be incredibly hard for Democrats to knock off.

Not ranked: Arizona or Ohio

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