(CNN) Donald Trump's campaign manager and running mate said Sunday the GOP candidate doesn't want Gennifer Flowers -- who had an affair with Bill Clinton in the 1970s -- at Monday night's presidential debate .

"We have not invited her formally, and we do not expect her to be there as a guest of the Trump campaign," Trump campaign manager Kellyanne Conway told CNN's Jake Tapper on "State of the Union."

Indiana Gov. Mike Pence, Trump's vice presidential nominee, told "Fox News Sunday" host Chris Wallace that Trump's suggestion he'd invite Flowers was just "mocking" Clinton's campaign for distracting from the real issues at stake on Monday night.

Their comments come after Trump tweeted that he was considering inviting Flowers to sit in the front row for the first debate.

The back-and-forth about Flowers comes as a new poll shows the race is dead even going into a debate that's expected to be the biggest in history -- with 100 million or more viewers -- and another survey finds as many as one-third of voters say the first face off will be key to their decisions on who to support in the 2016 presidential race.

Trump brought up Flowers after Mark Cuban -- the billionaire owner of the NBA's Dallas Mavericks and a Trump critic -- tweeted that he'd been invited by Clinton's campaign to sit in the front row at the debate.

Just got a front row seat to watch @HillaryClinton overwhelm @realDonaldTrump at the "Humbling at Hofstra" on Monday. It Is On ! — Mark Cuban (@mcuban) September 23, 2016

In a response on Twitter, Trump mocked Cuban's short-lived reality TV show "The Benefactor" -- which was similar to Trump's "The Apprentice." (Cuban is now featured on a more successful reality show, "Shark Tank.")

Trump wrote: "If dopey Mark Cuban of failed Benefactor fame wants to sit in the front row, perhaps I will put Gennifer Flowers right alongside of him!"

If dopey Mark Cuban of failed Benefactor fame wants to sit in the front row, perhaps I will put Gennifer Flowers right alongside of him! — Donald J. Trump (@realDonaldTrump) September 24, 2016

The New York Times reported that Flowers told the newspaper in a text message, "Yes I will be there."

However, Conway denied that Trump's campaign had invited Flowers -- whose affair with Clinton was revealed in the 1990s -- and blamed Clinton's campaign for the topic even coming up, saying the former secretary of state was "easily baited."

Asked if Trump will raise the Clintons' marital history or Bill Clinton's affairs in the debate, Conway said "there's no plan to do that."

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"Mr. Trump will answer the questions as they are asked by Lester Holt, the moderator, and he has a right to defend himself against anything Mrs. Clinton -- Secretary Clinton -- may say in response," Conway said.

It's not the first time Trump has raised Bill Clinton's marital affairs in political attacks on Hillary Clinton. He did so repeatedly as she clinched the Democratic nomination, accusing Hillary Clinton of mistreating the women involved in her husband's affairs.

Clinton campaign manager Robby Mook told Tapper on "State of the Union" that the episode reflected Trump's broader campaign.

"It's a warning sign before the debate has even started about Donald Trump's lack of fitness -- his bullying tactics -- that make him unfit to be president," Mook said.

Clinton's invitation to Cuban -- a billionaire who has questioned Trump's wealth, suggest the billionaire's "dream scenario" is to lose the election, and has cast Trump as substance-free -- and the GOP candidate's raising of Flowers comes as the candidates play head games ahead of the debate.

Wall Street Journal/NBC News poll shows that one-third of voters say the debate will be "extremely" or "quite" important in their decision on who to support for president.

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The two enter the debate virtually tied. An ABC News/Washington Post poll shows Clinton's lead is 2 percentage points -- with likely voters split 46% for Clinton, 44% for Trump, 5% supporting Libertarian Gary Johnson and 1% for the Green Party's Jill Stein. That's well within the poll's 4.5 percentage point margin of error.

Clinton's debate prep sessions Saturday went late into the night, with her motorcade only returning to her Chappaqua, New York, home at 11:45 p.m. ET.

Clinton, along with her top aides, is continuing debate preparations on Sunday at a hotel and conference center in Rye Brook, New York, while both she and Trump are separately meeting with Israeli Prime Minister Benjamin Netanyahu. In Clinton's debate prep sessions, Trump is being played by Philippe Reines, the combustible long-time aide.

Clinton running mate Tim Kaine said the former secretary of state will defend herself from Trump and "paint this positive vision that really is what's animating her to run for president."

The Virginia senator said the debate will offer voters a window into whether the candidates' remarks come with depth and truthfulness.

"In a 90-minute format, not 20-second sound bites, there's a real opportunity to hear somebody say something and then get into, 'Is that actually true or not?'" Kaine told CBS' John Dickerson on "Face the Nation" Sunday. "So I think the debate issue, you know, obviously let it be an even standard for both. But that issue about specifics, answering those unanswered questions and checking people on truthfulness -- that's going to be very important."

Former New York City Mayor Rudy Giuliani, who was at Trump Tower on Sunday to help Trump with debate prep, said they aren't doing mock debates -- "we go over issues."

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"We'll do some more strategizing about what I think will be probably one of the most important presidential debates in American history. The Nixon-Kennedy was the most famous, but this will have an audience that is far greater," Giuliani said.

He predicted Trump will do "very, very well," and that Trump doesn't want to be over-rehearsed.

"If you got to over-prepare, you over-prepare. But if you have confidence in yourself, you go with what got you there," Giuliani said.

He took a shot at Clinton, too, for spending several days focused largely on preparing for Monday night's first of three presidential debates.

"Looks to me like she hasn't appeared for about four days. Hope everything is OK, and I wish her well," Giuliani said. "I think if I spent as much time inside as she does I'd go stir crazy. So that's me. Everybody is different."

House Speaker Paul Ryan said on CBS' "Face the Nation" that Trump should "over-prepare" for Monday night.

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"Look, Hillary Clinton's been doing this most of her life. She is the consummate pro. This is new for Donald," Ryan, R-Wisconsin, told host John Dickerson.

"So I think he should obviously over-prepare for it. ... You have to offer the country a vision, go on offense, prosecute your case, hold your opponent accountable," Ryan said. "But then show the country the direction you want to go -- and prepare, prepare, prepare. And I hope he's doing that."

Ahead of the debate, Clinton's campaign also launched a new attack ad , suggesting Trump's refusal to release his tax returns is linked to his Russian business ties. The ad is airing nationally on cable TV.

Clinton press secretary Brian Fallon appeared on CNN's "Reliable Sources," where he reiterated the campaign's call for fact-checking at the debate.

"If you have a moderator that takes a hands off approach, and says that they are not going to fact-check the candidates, that they are going to sit there and close their ears to Donald Trump's lies, it will extend an unfair bias to Donald Trump. It will be the equivalent of giving him for time to speak," Fallon said.

Fallon cited Trump's frequent, false claim that he opposed the Iraq War from the beginning, and said, if Trump lies about his position on the Iraq War, "(Moderator) Lester Holt should follow up."

He also took a dig at Conway, saying she "will breathe a sigh of relief probably if he (Trump) gets through 90 minutes without having a meltdown."