Senate leaders could be guessing who will control the chamber well into November, thanks to a slew of tight races and state-specific voting rules.

Why it matters: A GOP majority would ease the pressure on Senate Majority Leader John Thune to move quickly on nominations, while a Democratic majority would give Senate Minority Leader Chuck Schumer more leverage in the lame-duck session.

• If the chamber splits 50/50, leaders will have to start negotiating their power-sharing agreement.

Zoom in: Four states could leave the majority in limbo.

• Alaska: Sen. Dan Sullivan (R) is trying to fend off former Rep. Mary Peltola (D). Alaska election results have taken weeks to finalize because of the vast state's transportation challenges, mail ballots and ranked-choice tabulation. The Trump Justice Department is preemptively trying to block results from being finalized if Sullivan narrowly loses.
• Maine's ranked-choice voting could lengthen the vote tallying if neither Sen. Susan Collins (R-Maine) nor Democratic nominee Troy Jackson gets more than 50% in the first round.
• Kansas' three-day grace period for mail-in ballots could delay results in the race between Democratic nominee Adam Hamilton and Sen. Roger Marshall (R-Kan.). It is far closer than expected.
• In Texas, a dragged-out recount could be coming. A candidate can request one if the margin is less than 10% of the winner's vote total — which is likely to happen between state Attorney General Ken Paxton (R) and state Rep. James Talarico (D). The candidate who requests it has to pay.

The clock: Congress currently plans to leave for the holidays on Dec. 18.

• But if Republicans lose both the House and Senate, Sen. Bernie Moreno (R-Ohio) wants senators to stay in town through the holidays (yes, Thanksgiving and Christmas) to work on a massive GOP reconciliation package they can pass without Democratic support.

The big picture: Congress has a long to-do list either way, including funding the government past Dec. 11, passing emergency defense spending and potentially raising the debt ceiling.

• It needs to pass the National Defense Authorization Act, Farm Bill and permitting reform, reauthorize the warrantless wiretap authority under FISA Section 702 and confirm nominations before they expire at the end of the year.

The bottom line: "I'm guessing that's a possibility this year," Sen. Cynthia Lummis (R-Wyo.) told reporters today about working in D.C. through the holiday recess.

— Stef Kight

From Johnny Manziel to former President Obama, big names are hitting the campaign trail in the next few days to rally voters in key Senate battlegrounds.

Why it matters: There are now seven Senate races considered "toss-ups" by Cook Political Report. That's a huge map to cover for get-out-the-vote rallies in the final stretch.

• Today in Ohio: Singer John Legend rallies with Democratic Senate nominee Sherrod Brown.
• Today in Mississippi: Trump flies in to campaign for Sen. Cindy Hyde-Smith, whose race has become surprisingly close (but is still rated "likely Republican").
• Tomorrow in Texas: Former Texas A&M QB Manziel, former Texas QB Colt McCoy and former Texas Tech WR Danny Amendola join Trump at campaign rallies across the state, as Axios' Alex Isenstadt scooped today.
• Wednesday in Ohio: Singers Matt Berninger and Aaron Dessner of The National rally with Brown.
• Wednesday in Georgia: Former President Obama rallies with Sen. Jon Ossoff in Atlanta.

Flashback: Singer Nicki Minaj joined Trump to rally for GOP nominee Mike Rogers in Michigan, while actress Eva Longoria rallied for Talarico in San Antonio on Saturday. Obama joined Democratic nominee Abdul El-Sayed at a Michigan rally.

— Justin Green