Here’s your guide to help track and understand what wins in losses in various House races mean for the balance of power in Congress:

First of all, keep in mind how rare it is for the House to switch hands. It’s changed party control three times since 1954. The Democrats won in 1954 and held it until the Republican revolution in 1994, ushering former House Speaker Newt Gingrich, R-Ga., to power. Democrats won in 2007, sending making current House Minority Leader Nancy Pelosi, D-Calif., first female speaker in U.S. history. Republicans won the House back in 2010, winning a net of 63 seats.

To many on the left, the 2018 midterms are about avenging what happened in 2016. Democrats and progressives are eager to counter-balance the influence of President Trump. They want to repudiate the president with big wins in the House, portraying Trump’s 2016 victory as an Electoral College fluke.

Multiple political experts eschewed the concept of a “wave” election in favor of the Democrats. If Democrats are successful and win the House, the terms “reset” or “realignment” may be a more accurate description of the midterms – especially in the House.

An alarming number of retirements by House Republicans gives Democrats their best chance in a decade to take the House. But such a victory is far from guaranteed. Republicans are confident that their party will see at least a net loss of 18 seats. Democrats need to win 23 seats to claim control. So, if the House remains Republican, it’s going to be tight. If Democrats win the House, the margin is likely to be tight, too.

There’s a decent chance voters could decide a lot of seats by a percentage point or less. That could trigger recounts and canvassing of provisional ballots. It’s possible control of the House could swing in the balance for a few days if things are close.

That said, there are some geographical markers to watch for – starting in the east – which could yield clues as to how the night may go.

Let’s start in northern Maine. Rep. Bruce Poliquin, R-Maine, faces Democrat Jared Golden in a district which favors Republicans by just two percentage points. Poliquin is the only remaining Republican in New England, flipping the district from blue to red in 2014. Maine proportionally allocates its four Electoral College votes. Hillary Clinton secured three of the four, as President Trump captured one of the two electoral votes in Poliquin’s district.

Another wrinkle.

Maine now features “ranked choice” voting. Two other candidates are in the race besides Poliquin and Golden: independents Tiffany Bond and Will Hoar. Under the ranked choice, system, voters cast ballots for their first choice. But if no candidate marshals 50 percent of the vote, a candidate’s second choice is counted as a vote in favor of the first choice.

The 50 percent rule is important. Poliquin won with just 47 percent in 2014.

As we move south, Democrats should have a good night flipping a host of seats in Pennsylvania, New Jersey, and, to a lesser degree, upstate New York. It’s a good sign for Republicans if Rep. Claudia Tenney, R-N.Y., holds her seat.

Also in New York, watch the race between Rep. Chris Collins, R-N.Y., and Democratic nominee Nate McMurray. Handicappers expect Collins to win – despite an August indictment for alleged securities fraud and insider trading.

For a moment, zip out to California. There could be the same problem with Rep. Duncan Hunter Jr., R-Calif., who is also under indictment.

Republicans will have to address these ethics issues if either or both Collins and Hunter win re-election. Democrats will be sure to make a lot of noise about these seats, too.

Perhaps the “swingiest” district in the country is held by retiring Rep. Carol Shea-Porter, D-N.H. With the exception of 2008, that seat has gone Republican in every off-year election since.

Other bellwethers to watch: it’s probably not going to be a good night for Republicans if Democrat Richard Ojeda tops Republican Carol Porter in southern West Virginia. Rep. Evan Jenkins, R-W.Va, is vacating that seat after losing the Senate GOP primary. That seat was in Democratic hands for years, represented by former Rep. Nick Rahall, D-W.Va. Trump won that seat by an eye-popping 49 points.

It’s probably not going to be a good night for Republicans if Democrats win key seats in Virginia, upending Reps. Barbara Comstock, R-Va., and Dave Brat, R-Va., with Democrats Jennifer Wexton and Abigail Spanberger. It will be a very bad night if Democrat Leslie Cockburn defeats Republican Denver Riggleman in the seat held by retiring freshman Rep. Tom Garrett, R-Va.

It could be a good night for Republicans if Rep. Ted Budd, R-N.C., holds on as well as Reps. Carlos Curbelo, R-Fla., and Mario Diaz-Balart, R-Fla. The key House race in Florida though is the seat held now by retiring Rep. Ileana Ros-Lehtinen, R-Fla. Hillary Clinton carried that seat by 19 points. Republican Maria Elvira Salazar is up against Democrat Donna Shalala, the Health and Human Services Secretary in the Clinton administration.

Keep an eye on Rep. Steve Chabot, R-Ohio, is running against Democrat Aftab Pureval. We also have a rematch of the August special election in central Ohio between GOP Rep. Troy Balderson and Democrat Danny O’Connor. Balderson bested O’Connor by about 1,500 votes in August.

Republicans are in deep trouble if you see issues with veteran Reps. Rob Woodall, R-Ga., Fred Upton, R-Mich., or French Hill, R-Ark.

Also out west, the GOP could face problems nationwide if House Republican Conference Chairwoman Cathy McMorris Rodgers, R-Wash, Jaime Herrera Beutler, R-Wash., and Rep. Don Young, R-Alaska, struggle. Young is the most-senior member of the House, first elected in a special election in 1973.

Also, one state to watch in particular: Nevada: Rep. Jacky Rosen, D-Nev., is running for Senate and vacating the seat after one term. Democrat Susie Lee is pitted against Republican Danny Tarkanian, the son of the famous UNLV basketball coach Jerry Tarkanian. The seat went for President Trump by a single percentage point. Tarkanian kept Rosen under 50 percent in that district two years ago.

Also, former Rep. Cresent Hardy, R-Nev., is up against former Rep. Steve Horsford, D-Nev. Hardy defeated Horsford in an upset in 2014. Rep. Ruben Kihuen, D-Nev., then beat Hardy, but is now retiring.