The Pa. GOP Senate front-runners will debate for the first time. How to watch and what to watch for.

Mehmet Oz and David McCormick have been all over Pennsylvania television, but rarely on the same stage together.

That changes Monday night, when the top Republican candidates for U.S. Senate debate at ABC27 studios in Harrisburg, a face-off airing on TV stations statewide and streaming online.

Front-runners Oz and McCormick will be joined by Kathy Barnette, Jeff Bartos, and Carla Sands. Although Oz and McCormick both participated in a forum in Erie earlier this month, this will be the first time the two are together in public for a formal debate after they spent millions of dollars each to promote their candidacies with TV ads.

The debate comes two weeks after former President Donald Trump endorsed Oz, the celebrity surgeon known as “Dr. Oz,” and as polls show him and McCormick locked in a tight race for the nomination.

» READ MORE: What Trump’s Mehmet Oz endorsement means for the Pennsylvania Senate race

Pennsylvania’s Senate race is one of the most crucial in the country, likely to help decide control of the chamber, and with it, the fate of much of President Joe Biden’s agenda after this year.

How to watch: The one-hour debate will air on eight television stations across the state, including WPHL-TV (PHL-17) in Philadelphia. It will be live-streamed on WETM-TV (NBC) in Elmira, N.Y., WPIX-TV (CW) in New York City, WIVB-TV (CBS) in Buffalo, and WDVM-TV (IND) in Washington.

Who: Kathy Barnette, Jeff Bartos, David McCormick, Mehmet Oz, and Carla Sands.

When: 8 p.m. Monday, April 25.

Where: ABC27 Studios in Harrisburg.

Moderators: Dennis Owens, WHTM ABC27 news anchor and Capitol Bureau reporter, and Lisa Sylvester, WPXI anchor.

Even though Oz and McCormick, a former hedge fund CEO, are running close in polling, the TV celebrity drew the most heat when the candidates got together in Erie earlier this month. Oz seemed almost taken aback by the hits, while McCormick, despite by some accounts being the front-runner, walked away virtually untouched.

In some ways, it makes sense: Oz is a famous name, so taking him on might draw his critics more attention. But the underdogs also can’t afford to just give McCormick a pass.

Is Oz more ready for attacks this time? And as his rivals accuse him of being a liberal masquerading in a GOP primary, can he use the Trump endorsement to fend off their attacks and convince conservative voters that he’s one of them?

For a guy near the top of the polls, McCormick hasn’t been very visible in his own campaign. He has largely campaigned by buying up TV ads and by appearing alongside more famous supporters, such as Sen. Ted Cruz and former Secretary of State Mike Pompeo.

But up on stage by himself, how does McCormick hold his own against his rivals? Do they challenge him or stay focused on Oz? And does he still claim to carry the “America First” mantle now that Trump has chosen a different candidate?

The free-spending front-runners have overshadowed everyone else in the field. The other contenders’ hopes seem to hinge on those two punching each other out, clearing a path for a third candidate to sweep into victory. But for that to happen, Barnette, Bartos or Sands has to become established as the clear alternative.

Without the money to really compete on TV, this is one of their few chances to stand out in front of a significant GOP audience.

Barnette has been a sharp debater, with hard-hitting delivery in previous events, while Bartos has been self-deprecating about his mild demeanor, aiming to impress more by recounting his grassroots campaigning. Sands has been less visible on the campaign trail, but has a chance to make a wider impression tonight.

Over the last few weeks, financial disclosures have offered the first public looks at the immense personal wealth that Oz and McCormick are bringing to this race, including each owning multimillion dollar homes scattered across the country. But they purchased primary Pennsylvania residences only in the last six months (though McCormick has long owned his family farm in the state, and Oz says he has been renting his in-laws’ Montgomery County home since late 2020).

Do their rivals make an issue of it?