After a year and half of wondering which senators might retire, if the parties would land star recruits, and how messy primaries would play out, the matchups in nearly all of the most competitive Senate races will be set after the votes are counted in Montana on Tuesday.

Republicans in Big Sky Country are likely to select either state Auditor Matt Rosendale or former district judge Russ Fagg to take on Democratic Sen. Jon Tester, leaving just a couple of unknowns on the broader Senate map, five months before Election Day.

Of course, not all states have held their primaries yet, but in most of those contests, the likely nominees are clear, even though some of the favorites have opponents.

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Voters in North Dakota and Nevada will select nominees next week, on June 12. But GOP Rep. Kevin Cramer is the likely party choice to take on Democratic Sen. Heidi Heitkamp in the Peace Garden State, while Rep. Jacky Rosen is the likely Democratic nominee against Republican Dean Heller in the Silver State.

Four more states will officially select nominees later in the summer, but the Senate matchups are all but certain.

GOP Rep. Marsha Blackburn is likely to face off against former Democratic Gov. Phil Bredesen in Tennessee (Aug. 2 primary). State Attorney General Josh Hawley is the likely GOP nominee against Democratic Sen. Claire McCaskill in Missouri (Aug. 7 primary). State Sen. Karin Housley received the Republican Party endorsement on Saturday and is the likely GOP nominee against appointed Democratic-Farmer-Labor Sen. Tina Smith in Minnesota (Aug. 14 primary). And Gov. Rick Scott will be the Republican nominee against Democratic Sen. Bill Nelson in Florida (Aug. 28 primary).

Primaries are completed in West Virginia (where Democratic Sen. Joe Manchin faces Republican state Attorney General Patrick Morrisey), Indiana (Democratic Sen. Joe Donnelly vs. former GOP state Rep. Mike Braun), Ohio (Democratic Sen. Sherrod Brown vs. GOP Rep. James B. Renacci), Pennsylvania (Democratic Sen. Bob Casey vs. GOP Rep. Lou Barletta) and Texas (GOP Sen. Ted Cruz vs. Democratic Rep. Beto O’Rourke).

The two biggest question marks remaining on the Senate side are Arizona and Wisconsin.

Rep. Martha McSally is the Republican front-runner for the seat Arizona GOP Sen. Jeff Flake is vacating. But according to public polling, she’s leading the primary field with less than 50 percent against former state Sen. Kelli Ward and former Maricopa County Sheriff Joe Arpaio. If Arpaio or Ward were to drop out before the Aug. 28 primary, that could consolidate anti-establishment voters behind the remaining candidate and complicate McSally’s path. Rep. Kyrsten Sinema is the likely Democratic nominee.

Wisconsin Republicans will choose a challenger to Democratic Sen. Tammy Baldwin on Aug. 14. The nominee will likely be either state Sen. Leah Vukmir or businessman Kevin Nicholson. Donald Trump was the first GOP presidential nominee to win the Badger State since Ronald Reagan’s re-election in 1984, but whoever wins the GOP nod would start as an underdog against Baldwin.

The biggest unknown of the Senate map could be Mississippi, where all candidates for former Republican Sen. Thad Cochran’s seat will run together on a nonpartisan ballot on Nov. 6. If appointed GOP Sen. Cindy Hyde-Smith, Republican state Sen. Chris McDaniel and former Democratic Rep. Mike Espy fail to top 50 percent, the race will move to a Nov. 27 runoff.

That means if a Republican and Espy move on, and the Senate majority hinges on one seat, Thanksgiving will be prime time for turkey, stuffing and Mississippi campaigning.