There are a number of reasons why it may take a while to know which party will control Congress next year, including laws that restrict when officials can start processing mail-in ballots, close races triggering automatic recounts and the idiosyncrasies of 50 different election systems, each with its own rules.

There’s also the potential for chaos brought on by some Republican candidates who, spurred by former President Donald Trump, have already said they won’t abide by the results unless they win. 

[If control of the House is close, Jan. 3 could be chaos]

A lot will depend on how close races are. California has six districts with race ratings of Lean, Tilt or Toss-up, according to Inside Elections, and the state routinely takes days to tally all its votes. The 2020 win by Republican Rep. David Valadao, who ousted Democratic Rep. TJ Cox by 1,522 votes and is in another Toss-up race this year, was not called until Nov. 27. 

Maine and Alaska, which each has House races that are competitive, use ranked-choice voting if a candidate does not get more than 50 percent. In Alaska, they wait 15 days after the polls close to do the ranking to ensure that all ballots mailed or cast in remote areas arrive to be counted.

And calling which party wins the majority in the Senate could take days — or even weeks. Close races in Pennsylvania, Wisconsin and Arizona will certainly stretch beyond Tuesday because those states won’t start counting mail-in ballots until Election Day. The hard-fought battle in Georgia between Democratic Sen. Raphael Warnock and Republican Herschel Walker likely will not be decided until a Dec. 6 runoff in part because the Libertarian Party candidate has been consistently polling at 2 percent to 3 percent, enough to deny either major-party candidate 50 percent. 

Despite those caveats, some early results from the East Coast will offer important clues about which party is in line to control the House and the Senate for the next two years. Here are some bellwether races and when all polls will close, in Eastern Standard Time, in those states.

7 p.m.: Virginia and Indiana

Virginia has several races that could signal fairly early whether Republicans are having a good night, or if Democrats might buck predictions and hold on to House control. Three members of the blue wave class of 2018 — Elaine Luria, Abigail Spanberger and Jennifer Wexton — all are facing strong GOP challenges. Luria, who is running against Republican state Sen. Jen Kiggans in the 2nd District, is one of the party’s most vulnerable incumbents. If Luria were to win, it would be a sign of Democrats overperforming expectations. Losses by Spanberger and especially Wexton, whose Northern Virginia seat is considered safer for Democrats, would suggest “a huge night” for Republicans, said CQ Roll Call elections analyst Nathan L. Gonzales.

In Indiana, Democrats have held the 1st District for more than 90 years, but Republican Jennifer-Ruth Green is hoping to change that. Green, an Air Force veteran, is seeking to unseat Democratic Rep. Frank J. Mrvan. A win by the GOP in this northwestern Indiana district could be a harbinger of Republican dominance.

7:30 p.m.: North Carolina

A strong showing by Democratic candidate Cheri Beasley in the race for an open Senate seat against Republican Rep. Ted Budd could signal a good night for Democrats. “If Beasley wins, or even if it’s extremely close, it could be a sign that Democrats are holding their own,” Gonzales said. The outcome of a competitive race in the open 13th District, a newly redrawn swing seat that encompasses the Raleigh suburbs and several rural counties, could provide a hint about the strength of the Trump wing of the party. Republican Bo Hines, an ex-college football player who has embraced the MAGA label, is facing Democratic state Sen. Wiley Nickel.

8 p.m.: New England

The winners of two House races in southern New England, Rhode Island’s 2nd District and Connecticut’s 5th District, could provide a fairly early indication of whether the GOP succeeds in moving into blue states. Both parties and super PACs affiliated with their congressional leaders have invested heavily in these two races, particularly in Rhode Island, where former Cranston Mayor Allan Fung, a Republican, is running against state Treasurer Seth Magaziner for the open seat. Fung and George Logan, the GOP nominee in the Connecticut race, have cast themselves as moderates focused on fiscal issues, not social ones. Magaziner and Democratic Rep. Jahana Hayes, Logan’s opponent, portrayed the Republicans as allies of election deniers and extremists.

Sen. Rick Scott of Florida, chairman of the National Republican Senatorial Committee, says he’ll be looking further north, to New Hampshire, for an early indication of how the night is going. “Don Bolduc beats Maggie Hassan, that’s the precursor to what’s going to happen across the country,’’ Scott said, referring to the Senate race between Democratic Sen. Maggie Hassan and Republican retired Army Brig. Gen. Don Bolduc.