PHILADELPHIA — Tonight’s big races in Pennsylvania and North Carolina are sending tremors across the Republican Party, as its MAGA wing vies for dominance with other flavors of Trumpism.

Democrats have held quieter primaries, but their party’s center-left establishment has battled progressive uprisings in places like the Raleigh-Durham region and Pittsburgh.

New York Times reporters have fanned out across the states, and polls close in Pennsylvania at 8 p.m. Eastern and in North Carolina at 7:30 p.m. Eastern. Follow our live coverage of developments here, and view the results as they come in here. For now, we’ve got some questions about the wider implications of today’s races:

Will Kathy Barnette claim the election was stolen if she loses?

Barnette, a conservative commentator, has rocketed toward the top of polls in the Republican primary for Senate in Pennsylvania.

She rose to prominence for embracing conspiracy theories about the 2020 election — including ones about her own failed race that year for a House seat in the Philadelphia suburbs, which she lost by nearly 20 percentage points to Representative Madeleine Dean, the Democratic incumbent. Barnette refused to concede, despite no evidence of problems with the election.

The campaigns for Barnette’s top rivals, Dr. Mehmet Oz and Dave McCormick, projected confidence in conversations with senior campaign aides and surrogates today, but both are bracing for the possibility that Barnette will make similar claims if tonight’s results are especially close or uncertain.

“We’re focused on running our race and we’re confident that Kathy will have a good night,” said Ryan Rhodes, a spokesman for the Barnette campaign.

The McCormick campaign, which has the largest legal and communications infrastructure of all its rivals, has deployed 500 poll monitors to watch for any irregularities.

Barnette’s late surge has frazzled and dismayed Republicans in Pennsylvania and beyond. They fear that her biography has not been subject to serious scrutiny, and many G.O.P. operatives in Washington would prefer Oz or McCormick, who are widely deemed better candidates for the general election.

Republican strategists are weighing how to respond if the results tonight are close. Some counties are not expected to begin counting mail-in ballots until tomorrow.

“If Kathy alleges fraud, I hope it will be for good reason,” said Josh Novotney, a Philadelphia-based lobbyist for SBL Strategies. “If not, it will hurt our party.”

“A candidate crying election fraud against a Trump-backed candidate will probably have to be put in Webster’s as the new definition of irony,” he added.

How does the progressive movement fare?

Not every Democratic primary today falls neatly into the bucket of progressives versus the establishment. But there are few exceptions.

One House primary in Oregon stands out because it’s not for an open seat. The incumbent, Representative Kurt Schrader, a leading moderate, has support from House Democrats’ campaign arm and an endorsement from President Biden.

In Congress, progressive leaders haven’t flocked to support his challenger, Jamie McLeod-Skinner. But she has received the backing of one prominent Democrat — Senator Elizabeth Warren — as well as support from smaller left-leaning groups and several county Democratic Party organizations in Oregon that would normally be expected to back the incumbent or remain neutral.

The clearest example of a left-versus-center showdown might be in Pittsburgh, where Representative Mike Doyle, a Democrat, is retiring. The top contenders to replace him are Summer Lee, a state legislator backed by progressives including Warren and Senator Bernie Sanders, and Steve Irwin, a Democrat supported by Doyle.

“It’ll be a real bellwether for where the progressive movement is today,” said Aren Platt, a Democratic strategist in Pennsylvania.

The United Democracy Project, a super PAC affiliated with the American Israel Public Affairs Committee, aired an ad that questioned Lee’s loyalty to Biden and the Democratic Party. The progressive group Justice Democrats has also been on air questioning whether Irwin is a “real Democrat” by trying to tie him to Republicans.

In another twist that could potentially be confusing for voters, the Democratic nominee will face Mike Doyle — not the departing Democratic congressman, but a Republican who serves as president of the Plum Borough Council. Marc Elias, the well-known Democratic elections lawyer, sought unsuccessfully to have the Republican Doyle removed from the ballot.

What defines a North Carolina Republican?

There are a lot of personalities — and a lot of money — in the Republican primary races in North Carolina.

For Representative Ted Budd, the front-runner for the G.O.P. nomination in the Senate primary, the race has been all about Trump — and it’s impossible to ignore the substantial boost he received from the Club for Growth, an influential anti-tax group.

Budd’s top opponents have sounded much more like typical North Carolina Senate candidates. For Pat McCrory, a former Republican governor, the election has been all about inflation and conservative economic policies. Mark Walker says it’s about “the Bible and the Constitution.”

In House races, Republicans are running candidates like Representative Madison Cawthorn, who has an ever-lengthening list of scandals to his name, and Bo Hines, who has gone all in on calling his opponents Marxists and RINOs.

But drawing any firm conclusions from these races about the state of Republican politics in North Carolina or nationally is a fraught business, said Jordan Shaw, a Republican strategist who works with candidates in the state.

“There’s been so much money spent in this primary on selected races, I think it’s hard to paint it with a wide brush because it’s been such a money bomb here in North Carolina,” said Shaw, who works with McCrory.