Tuesday's Pennsylvania primary election comes as Democrats eye the Keystone State as a critical piece of their hopes to win control of the U.S. House this fall, with the results tonight setting the stage for what could be some of the country's toughest congressional races.

There are nomination battles in several competitive contests (mostly on the Democratic side), a potential demonstration of Trump's imprint on the Pennsylvania GOP and a test of whether Bernie Sanders can translate supporters' enthusiasm into victories for his allies.

Here are several key races and themes we will be watching as the returns come in:

Can women break through?

Democrats hope it will be the "Year of the Woman," especially in the suburbs where women have fueled a revolt against Trump. But Pennsylvania is a notoriously unfriendly place for female politicians: the state's 20-person congressional delegation is entirely male. Will that change this year? Some women are all-but assured of their party nominations, since they are running unopposed (including Democrats Chrissy Houlahan in Chester County and Republican Pearl Kim in Delaware County). In several other contests, however, including races based in Bucks, Delaware, Lehigh and Montgomery counties, Democratic women are facing tough primary competition. The winners in some of those races will be heavily favored in the fall — which means today's results could go a long way to deciding if a woman, or multiple women, will be in the state's House delegation. EMILY's List, a group that backs Democratic women, has endorsed in several Pennsylvania races, and in some cases spent heavily.

Trump’s Imprint

The president takes particular pride in his 2016 victory in Pennsylvania, where he broke a long Democratic winning streak. Today may show just how much his influence has trickled down to other PA Republicans. Scott Wagner, a brash and confrontational businessman, and U.S. Rep. Lou Barletta, a close Trump ally who made his name as an illegal immigration hard-liner, are favored to win the GOP nominations for governor and U.S. Senate. (Trump recently recorded robocalls for Barletta, who was one of the president's most enthusiastic surrogates in 2016). Both Wagner and Barletta face challenges — from businessman Paul Mango and state Rep. Jim Christiana, respectively — but are favored. If they win, their nominations would mark a stark shift away from old methods and towards Trump. Consider that two years ago Sen. Pat Toomey refused to endorse Trump until hours before polls closed and spent millions depicting himself as an independent champion of compromise. At the time, many Republican insiders thought their best Senate nominee for 2018 might have been former U.S. Rep. Pat Meehan, who had a moderate profile that served him well in Delaware County (he declined to run, and revelations of a sexual harassment settlement pushed him to retire). With today's voting, the Pennsylvania GOP may instead affirm that in style, tone and priorities, it has wrapped its arms around Trump.

First Congressional District – Money vs. the Military

Democrats have a choice to make in this Bucks County-based swing district, where they hope to unseat Republican Rep. Brian Fitzpatrick. Scott Wallace, a liberal multi-millionaire and grandson of Henry Wallace, a vice president under  Franklin D. Roosevelt, is funding his own campaign and is favored. But he faces his stiffest challenge from former Navy prosecutor Rachel Reddick, who is one of several Democrats hoping that a military background can help them appeal to moderate voters. Environmentalist Steve Bacher is running from the left. Whoever wins is likely to have a tough — but winnable — fight on their hands in the fall, assuming Fitzpatrick survives a challenge from conservative attorney Dean Malik.

Fourth Congressional District – A Return for MontCo

Montgomery County will be all-but assured of sending a home-county representative to Congress thanks to this newly drawn district (a result of the Pennsylvania Supreme Court's new map). The Democratic race has drawn three high-profile candidates: state Rep. Madeleine Dean, who has racked up endorsements from high-profile party leaders; Shira Goodman, the leader of the gun control group CeaseFirePA, and former Congressman Joe Hoeffel, who represented the area years ago. Dean and Goodman have more money — and either would represent a win for suburban women — but Hoeffel's residual name recognition gives him a shot, and he says his previous congressional experience is critical in taking on the Trump administration. The winner will be heavily favored to go to Congress in the deep blue district.

Fifth Congressional District – Chaos and Opportunity

If any race captures the chaos of this year in Pennsylvania politics, it's this one. Through the combination of Meehan's sudden retirement and the new congressional maps, this district went from a Democratic long-shot to an almost sure gain in a matter of weeks — and drew more than a dozen contenders. Now 10 Democrats are left in a race that features an array of insiders, newcomers, DelCo hopefuls and a couple Philadelphians. Again there's a question of whether a woman can break through in a crowded field, and whether the many Delaware County residents will split the vote and open the door for Philadelphian Rich Lazer. The Democratic winner will almost certainly head to Congress in the fall, given the party's voter registration advantage. Though EMILY's List has weighed in elsewhere to help women, here, in perhaps the most competitive primary, the group was split between candidates Mary Gay Scanlon and Ashley Lunkenheimer, and so has not made an endorsement.

Seventh Congressional District — Wide Open

The battle for an open seat in the Lehigh Valley has exposed some of the jagged fault lines in the Democratic party.  It's the contest in this region that has the largest ideological divides, rather than simply biographical differences. Northampton District Attorney John Morganelli hopes his more moderate stances can appeal in this closely-divided swing district, home to the recently-resigned centrist Republican Charlie Dent. He can point to Democrat Conor Lamb's success in Southwestern Pennsylvania as a potential template. But his conservative stances on immigration and abortion worry much of the Democratic base. Sanders and the Congressional Black Caucus have endorsed Greg Edwards, while EMILY's List is behind Susan Wild. There's something for nearly every slice of the party here. On paper, the district looks like a competitive one in November, so the right nominee could make the difference.

Bernie’s Crew

Sanders is still playing on the national stage after sparking so much liberal enthusiasm in 2016, and has endorsed several candidates on the ballot today — hoping his energy can translate to potential allies. He's backing Lazer in the Fifth District primary, Edwards in the seventh and John Fetterman in the Democratic lieutenant governor race. Sanders also backed Jess King in the 11th District, where she is running unopposed. We'll see if Sanders can turn energy into tangible victories in tough races.