While much of the focus this midterm cycle has been on statewide races and the momentum behind Republicans amid dismal approval numbers for President Joe Biden, several Democratic House primaries could be emblematic of the direction of the party ahead of November.

In these contentious primary races in North Carolina, Oregon and Pennsylvania, voters will choose between progressive and more moderate candidates. These races have drawn the attention of progressive heavyweights, including Sens. Bernie Sanders and Elizabeth Warren.

Click here to read what you need to know about key Democratic House primary races, which include incumbent Rep. Kurt Schrader in Oregon gaining Biden's endorsement, and in North Carolina, Clay Aiken of "American Idol" fame taking another shot at Congress.

-ABC News Deputy Political Director Averi Harper

With primary day underway in some of the hottest races of the year, Rep. Conor Lamb, a moderate two-term Democrat vying for the U.S. Senate nomination in Pennsylvania, told ABC News' Senior Washington Reporter Devin Dwyer that results in the state Tuesday could be a key bellwether for the future direction of the party and control of the Senate.

"I think the Democratic Party is going to have to, you know, think really hard about how we're going to succeed and what is a very, very challenging political environment -- and today is going to have some lessons," Lamb said outside a polling place in his district.

Lamb, who has been trailing progressive Lt. Gov. John Fetterman in recent polls, acknowledged that Democrats face a choice between "two very different paths based on two different sets of experience and two different personalities," as many in the party view the race as their best shot at flipping a Senate seat.

Asked by ABC News whether he thinks Fetterman's hospitalization for a stroke will have any impact on the race, Lamb said "I don't know" and then offered what seemed to be criticism of his rival for "very little information about it [his condition] much like the rest of the general public."

"I wish him well, but I really can't forecast that and people are just got to make up their own minds," he said.

Two top Democrats in midterm races in Pennsylvania are facing health issues on primary day, causing them both to miss their election night events. One is isolated with COVID and another was in the hospital Tuesday undergoing surgery after a stroke.

Pennsylvania's Attorney General Josh Shapiro, who is running unopposed in the Democratic primary race for governor, announced this morning on Twitter that he tested positive for COVID-19 Monday night. He said he's isolated at home with "mild symptoms" and will be back on the campaign trail next week.

Shapiro also shared on Tuesday afternoon that he voted using an emergency absentee ballot, speaking in a video posted from his campaign's Twitter account.

Meanwhile, the front-runner in the Democratic Senate primary race, Lt. Gov. John Fetterman, underwent surgery on Tuesday to get a pacemaker and defibrillator after he suffered a stroke last Friday. As a result, his campaign team said he would not be able to attend his election night rally; instead, his wife, Gisele, will speak in his place.

Earlier on Tuesday, ahead of sharing the news of his surgery, Fetterman's campaign shared a photo of him voting via an emergency absentee battle in the hospital.

In a somewhat last-minute endorsement in April, former President Donald Trump threw his support behind Dr. Mehmet Oz in Pennsylvania's Republican Senate primary, citing the television doctor's popularity and compliments regarding Trump's health.

ABC News Congressional Correspondent Rachel Scott was the only network reporter with Dr. Oz as he voted this morning in Pennsylvania. On his way out, Oz told Scott he's confident he will win this evening’s primary. But a last-minute surge by conservative commentator Kathy Barnette has now shaken up the race.

When Scott asked Dr. Oz about her momentum, he said, "I think that Kathy, metaphorically, had her moment in the sun."

"And I'm very proud of the president's endorsement. He said I was smart-talking -- never let you down, smart enough to understand the issues tough, tough enough to not weather in the face of criticism. When you go to bed at night, you know, I'll never let you down," he added.

"I just cast a vote for myself, which is not a humble thing to do," Oz said. "But it's what I'm humbly asking all Pennsylvanians to do to vote for someone that they know will win in the general election which is one of the main reasons President Trump endorsed me."