WASHINGTON — Election Day is Tuesday, but with late votes and close races we might not know which party controls the House and Senate until the wee hours of the next day — or after. If you are watching closely, however, you can probably get a good idea of the way things are going early in the evening by keeping your eye on three states: Indiana, Kentucky and Virginia.

Results in key races in those states will likely offer strong clues about the fate of House and Senate control in 2019.

Indiana Senate — 6 p.m. ET poll close

The race here between Democrat Sen. Joe Donnelly and Republican businessman Mike Braun is listed as a tossup by the Cook Political Report and it’s worth watching for a few reasons.

First, Donnelly is an incumbent Democrat trying to win reelection in a state Republican Donald Trump won by 19 points in 2016. So the result may offer a larger clue about similar races in other Democrat/Trump states, such as Missouri and Montana. Second, in a broader sense, the outcome here could have a big impact on who ultimately controls the Senate. Republicans already have a 51-49 edge in the upper chamber, if they win here, they’ll be feeling good about growing that margin.

Republicans already have a 51-49 edge in the upper chamber, if they win here, they’ll be feeling good about growing that margin.

Not all polls close at 6 p.m. ET in Indiana — the northwestern and southwestern corners of the state close an hour later. On the early side, keep an eye on the vote in blue-collar Madison County, north and east of Indianapolis. Donnelly won it with 52 percent of the vote in 2012, but Trump won it with 59 percent in 2016.

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Kentucky’s 6th Congressional District — 6 p.m. ET close

In this district, which holds Lexington and much of the surrounding area, incumbent Republican Rep. Andy Barr is facing off against former Marine Corps pilot Amy McGrath. The race is currently rated a tossup by Cook.

Kentucky 6 will test a few important points Tuesday. The district sits in “red” Kentucky, but it’s home to two entities that could make it tough turf for Barr: The University of Kentucky, which is home to many younger, left-leaning voters, and the state capital of Frankfurt, the kind of place that tends to hold a lot of establishment Republicans who are not enamored with Trump.

The 6th also is known for producing a lot of bourbon — Woodford Reserve, Wild Turkey are based in the district — a liquor that was hit hard by Trump tariffs earlier this year.

If Barr loses here, it may be a sign of struggles for the GOP in other university/state capital districts around the country — Ohio 12, Pennsylvania 10, Michigan 8, Iowa 3 and Virginia 7. And rural agricultural counties hit by tariffs.

Virginia’s 2nd, 5th, 7th and 10th Congressional Districts — 7 p.m. ET close

Of all the early close states, Virginia is likely to tell us the most about the direction of the evening, at least where the House of Representatives is concerned. It is home to four Republican incumbent races that sit along different parts of the “possible flip” continuum.

Virginia 10 is the seat most likely to flip Democratic. Located in the Washington, D.C. suburbs, it’s currently held by Rep. Barbara Comstock, but rated “lean Democrat” by Cook. If the race is close, or if Comstock wins, that would be a good sign for House Republicans.

If the GOP loses here, it may be time for a blue wave watch.

Virginia 2 and 7 are both rated tossups by Cook. Both are above the national average for college degrees and home to smaller-city suburban populations — around Norfolk/Virginia Beach and Richmond respectively. If Democrats win in these districts, they might start measuring the drapes in the House Speaker’s office.

Virginia 5 is rated “lean Republican” and most years it would be the kind of seat the GOP wins easily. It’s rural and has voted for the Republican candidate in each of the past three presidential elections by comfortable margins. If the GOP loses here, it may be time for a blue wave watch.

These races won’t tell us everything, of course. Every contest is unique and, as any good campaign operative will tell you, candidates matter. The one big lesson out of 2016 is that surprises happen and there will probably be a few, or more than a few, in the 470 House and Senate elections Tuesday night — and don’t forget the gubernatorial and state house campaigns.

But if you’re looking for an early read on the evening, these three states should at least give a sense of which party has the upper hand going into the late-night hours.