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The presidential race shifts into high gear Tuesday night as Donald Trump and Kamala Harris hold their first and perhaps only face-to-face debate in Philadelphia.

With the race in a virtual dead heat, the stakes are high, both for the candidates and their supporters.

As narrow as the majorities are in both the United States House and Senate, members know the presidential race could influence who takes or retains control here come January. So, they say, tonight matters. "Every debate matters, right?" said Oklahoma Senator Markwayne Mullin (R-Okla.) in a Zoom interview Tuesday afternoon.

Mullin doesn't think the outcome of the race hangs on this one debate performance, but he believes it's important in showing voters who they're choosing between.

"I believe it's important for the American people to see the actual side of Kamala Harris and what she actually stands for," Mullin said, "because she's, you know, moved quite a bit and pivoted quite a bit."

Mullin, who traveled to Philadelphia to act as a Trump surrogate, says Harris is further to the left than Sen. Bernie Sanders. He believes former President Trump will make that clear in the course of the debate.

"He's taken this very seriously," said Mullin. "I know he's going to be focused on policy, I know he's going to be focused on delivering the message to the American people and exposing who Kamala Harris really is."

Democratic leaders expect Vice President Harris will lean into her experience as a prosecutor to go after Trump and detail the differences between the two. "A stark contrast in two candidates," said Rep. Pete Aguilar (D-Calif.), "one who's a seasoned prosecutor, who's going to make her case, and one who is a felon."

The 90-minute debate will have no studio audience, candidates are not allowed to have any pre-written notes on stage, and microphones will be muted when it's not the candidate's turn to speak.

Oklahoma Congressman Josh Brecheen (R-Okla. 2), a strong Trump supporter, says this should be an easy win for Trump.

"All that has to be done on the debate stage is the Reagan line: 'Are you better off?'" said Brecheen in an interview Tuesday, "except it's in reverse this time -- people know on those issues that you [were] better off four years ago."