5 things to watch in Tuesday's primaries in Maryland, West Virginia, and Nebraska

Even though the general election matchup is already set between President Joe Biden and former President Donald Trump, there have been plenty of fireworks down the ballot ahead of presidential and congressional primaries in Maryland, West Virginia, and Nebraska on Tuesday.

Downballot races in Maryland, for example, have led to bitter intraparty fights and questions over the role of spending in some races; while Senate primaries in West Virginia could offer a glimpse of who might replace retiring Democratic Sen. Joe Manchin. And Biden himself could face another protest vote in Maryland.

Here are 5 things to watch in Tuesday's races.

Who will triumph in the bitter Democratic Senate primary in Maryland, and what role will spending play in the race?

Democrats in Maryland are bracing for the end of what has become a bitter primary between frontrunner candidates Prince George's County Executive Angela Alsobrooks and Rep. David Trone, each of whom say they're the better bet to likely take on former Republican Gov. Larry Hogan in November.

Trone, the wealthy founder of Total Wine & More and a congressman in his third term, has injected over $50 million of his own money into the race and flooded local airwaves with advertising. He and groups supporting him have spent at least $45 million on ad reservations in the race, rapidly eclipsing Alsobrooks and groups supporting her, according to tracking from AdImpact.

But the congressman has said that the fact that he can self-finance his run allows Democrats to spend party money in races where they hope to flip seats or hold onto threatened ones. Speaking to reporters last Tuesday, Trone did not want to commit to not taking money from Democratic campaign committees, but said his self-funding "will give them a lot more flexibility to spend money elsewhere."

Alsobrooks, meanwhile, has some groups spending heavily to support her run. EMILY's List, a major political action committee that supports pro-abortion access female Democratic candidates, said it is spending over $2 million on airing ads criticizing Trone and has thrown its support behind Alsobrooks in the primary.

"She has a lived experience that is the voice we desperately need in the United States Senate," Jessica Mackler, president of EMILY's List, told ABC News in a recent interview.

How will Republican Senate candidate Larry Hogan perform in the Republican primary?

Whoever wins in the primary will likely face popular former Republican Gov. Larry Hogan, whose 11th-hour candidacy turned the race into one with major implications for which party controls the Senate. Hogan launched his Senate bid in February after flirting for months with a third-party presidential bid through No Label's now-discarded efforts to field a "unity ticket."

Political experts and observers have said that in spite of his name recognition, Hogan faces a steep uphill battle to flip the seat red -- given that Maryland is a deep-blue bastion.

During a brief interview with ABC News at an early voting location in Potomac, Maryland, Hogan acknowledged the challenge ahead. "I think we're arguably the bluest state in America … this will be the hardest challenge that I've ever had."

While Hogan is considered the frontrunner in the Republican primary, it may be worth watching how much vote he picks up from Republican primary voters, and how he does in some parts of the state. Hogan is a sharp critic of former President Donald Trump and presents himself as a moderate conservative – which puts him at odds with Trump's strong support among Republican primary voters.

"Tracking turnout among Republicans will be telling with regard to enthusiasm for Hogan," Michael Hanmer, ?the director of the University of Maryland's Center for Democracy and Civic Engagement, told ABC News. "A relatively high rate of turnout will be a clear signal in his favor given the lack of competition and his critiques of Trump."

Will heavy outside spending impact the race in Maryland's 3rd Congressional district?

Some Democrats in Maryland have raised concerns about how an outside group is spending millions in the race for Maryland's 3rd Congressional district -- with high-profile candidate and former Capitol Police officer Harry Dunn, who rose to prominence after being among the officers defending the U.S. Capitol on Jan. 6, calling the expenditures troubling.

The United Democracy Project (UDP), a super PAC affiliated with the American Israel Public Affairs Committee (AIPAC), has spent over $4.2 million in independent expenditures to support one of Dunn's primary opponents, state Senator Sarah Elfreth, according to FEC filings as of May 10. Those expenditures include direct mailings, media placement, media production, and phone banking.

UDP did not respond to a request for comment from ABC News about its spending in support of Elfreth, but the group told Jewish Insider in April that it is not targeting Harry Dunn specifically.

Dunn wrote in a statement in April, "Our grassroots movement won't be scared off by this dark money spending."

In response to a request for comment from ABC News about the expenditures from UDP and criticism from other candidates over them, Pat Murray, campaign manager for Sarah Elfreth's campaign, wrote that the campaign is proud of its many Maryland resident donors and support from progressive groups. "We are disappointed that other candidates launched last minute negative attacks, but that's a clear sign that they know Sarah is the frontrunner and in a strong position to win on Tuesday," Murray said.

Who will likely replace retiring Sen. Joe Manchin in Virginia?

The marquee race on Tuesday in West Virginia will be the GOP primary for U.S. Senate, where candidates are vying to replace retiring Sen. Joe Manchin, a Democrat. Republicans are eyeing the seat as a likely pickup.

The race could also be an indication of whether Republican voters are looking for candidates who frame. Current GOP Gov. Jim Justice, who has portrayed himself as experienced and who netted Donald Trump's endorsement, has a polling and slight fundraising advantage over U.S. Rep. Alex Mooney, who portrays himself as an anti-establishment candidate, ahead of their faceoff.

Before Manchin announced his plans not to seek reelection, the battle for West Virginia's Senate seat was shaping up to be one of the most competitive of the general election cycle. Now, national Democrats are largely remaining on the sidelines.

The Democratic Senatorial Campaign Committee is not endorsing in the race and Steve Daines, chair of the National Republican Senatorial Committee, called the November contest "over" in the majority-Republican state.

Will there be a major 'Uncommitted' protest vote against Joe Biden?

Activists have called on Democratic primary voters in some states to choose the "uncommitted" option on their ballot in states that include it, as a way to protest President Joe Biden's handling of the Israel-Hamas war and support of Israel.

There has been a similar organized effort in Maryland, where "Uncommitted to any Presidential Candidate" is an option on the Democratic presidential primary ballot. (Voters will also see Biden, author Marianne Williamson, and now-withdrawn candidate Rep. Dean Phillips.)

"We're urging people to vote 'uncommitted'… because the Biden Administration has not listened to the vast majority of the Democratic voters that want a cease-fire in Gaza," Anna Evans-Goldstein, an for the Listen to Maryland campaign, told ABC affiliate WMAR.

The Biden campaign told ABC News in a statement, "The President believes making your voice heard and participating in our democracy is fundamental to who we are as Americans. He shares the goal for an end to the violence and a just, lasting peace in the Middle East. He's working tirelessly to that end."

ABC News' Brittany Shepherd, Isabella Murray, Tal Axelrod, and Libby Cathey contributed to this report.