The GOP front-runners for Pa. governor finally debate tonight. How to watch and what to watch for.

Candidate forums in the Republican primary for Pennsylvania governor have been packed affairs, with two rows of podiums crammed onto stages to accommodate.

That changes Wednesday when only the four men polling at the top of the pack — former U.S. Rep. Lou Barletta, State Sen. Doug Mastriano, former U.S. Attorney Bill McSwain, and former Delaware County Council member Dave White — take the stage in a debate being broadcast from Harrisburg.

The stakes are high less than three weeks before the May 17 primary, with Barletta and Mastriano polling at about 20% in an average of surveys. A plurality of voters remain undecided.

And the Trump factor is still out there. An endorsement from former President Donald Trump could shake and shape the primary field. Trump has so far only ruled out a candidate, McSwain, in a stinging anti-endorsement that called McSwain a “coward” for not doing enough to investigate baseless claims of fraud in the 2020 election.

How to watch: The one-hour debate will air on eight television stations serving the state: WHTM-TV (ABC) in Harrisburg/Lancaster, Lebanon, and York, WPXI-TV (NBC) in Pittsburgh, WPHL-TV (MyNetworkTV) in Philadelphia, WTAJ-TV (CBS) in Johnstown, Altoona, and State College, WBRE-TV (NBC) in Scranton, Wilkes-Barre, and Hazleton, WJET-TV (ABC) and WFXP-TV (FOX) in Erie, and WYTV-TV (ABC) in Youngstown, Ohio.

Who: Former U.S. Rep. Lou Barletta, State Sen. Doug Mastriano, former U.S. Attorney Bill McSwain and former Delaware County Council member Dave White.

When: 8 p.m. Wednesday, April 27.

Where: abc27 Studios in Harrisburg.

Moderators: Dennis Owens, abc27 news anchor and Capitol Bureau reporter, and Lisa Sylvester, WPXI anchor.

With Trump’s endorsement still up for grabs, there’s a good chance the candidates will steer discussion about the upcoming primary election back to the 2020 presidential election.

A key element in Trump’s lies about that election is Act 77, the 2019 state law that vastly increased the use of mail ballots.

McSwain, campaigning as a first-time candidate in a field of “career politicians,” has been airing a television ad noting that Mastriano, like many Republicans in the state legislature, voted for the law.

» READ MORE: 4 takeaways from an earlier Republican debate for Pennsylvania governor

White has also campaign on repealing the law, but has focused his attacks more on State Senate President Pro Tempore Jake Corman, another candidate who voted for it and wants to repeal it — but won’t be on stage for Wednesday’s debate.

Mastriano and Corman have criticized how the law was implemented by Gov. Tom Wolf’s administration, and election-related rulings by the Pennsylvania Supreme Court that also affected its implementation.

The likely push-back: McSwain was the chief federal prosecutor in Philadelphia during the 2020 election and filed no cases alleging voter fraud.

Mastriano has come under renewed scrutiny for remarks he made in March 2020 demanding the government lift federal privacy protections and identify people who contracted COVID-19. “Failure to do this will put blood on their hands, and that’s pretty extreme, and I say that with seriousness,” Mastriano said at the time.

McSwain has been airing TV ads knocking Mastriano for that. And a well-funded conservative group called Commonwealth Leaders Fund is leveling similar attacks in mailers sent to primary voters. “Doug Mastriano wanted the government to expose our private medical data to the public,” the mailer says, according to one reviewed by The Inquirer.

Mastriano has made protecting personal freedom — including “medical freedom” from vaccine mandates — central to his campaign.

The campaign has rung with accusations of RINO — Republican In Name Only — as candidates present themselves as the only true conservative option.

Mastriano has been at the forefront in fighting his own party, especially Corman. He cast his campaign in biblical terms while speaking Saturday at a “Patriots Arise” event in Gettysburg.

“We’re sick and tired of settling for RINOs and the lies from our side of the isle, right?” Mastriano asked a cheering crowd.

McSwain has criticized White for taking government pandemic loans in 2020 for his business while self-funding his campaign now.

White has called McSwain’s campaign “flailing” since Trump renounced him.

While the primary has been contentious, the candidates find agreement in popular conservative culture war issues.

One favorite is vowing to ban “critical race theory” — a graduate-level academic field of study about how race factors into American institutions that has become a catch-all term for how race is taught in schools — in public elementary and high schools. It’s not actually taught there.

Corman, Montgomery County Commissioner Joe Gale, political consultant Charlie Gerow, former U.S. Rep. Melissa Hart, and cardiothoracic surgeon Nche Zama have participated in previous debates but weren’t invited to Wednesday’s event.

Nexstar, the corporation that owns abc27, set eligibility criteria in February for the debate. A key factor: Nexstar said it conducted a nonpartisan poll about one month before the primary, and candidates must have support from at least 5% of respondents.

Corman just missed the mark at 4%, while Hart and Gerow each received 3.1%. No one else broke 3%, and 27% of respondents were undecided.