WASHINGTON -?Hot-headed U.S. Republican candidate Donald Trump needs to show voters he can be calm and cool under pressure during Monday night's first presidential debate, U.S. experts said.

If Trump can do this, he may be able to continue closing in on his Democratic rival Hillary Clinton. If not, he may not be able to catch up, the experts said.

Trump has had a good run in the past few weeks, and has started to close Clinton's lead in the polls, as the controversial billionaire has toned down his rhetoric and focused on the issues in recent weeks.

Indeed, the brash businessman for the past year has become infamous for hurling insults at rival candidates and for what many critics call controversial and over-the-top statements. While that earned Trump much respect from his supporters, it has also alienated him from many independent and undecided voters.

But now, it is crucial for Trump during the debate to refrain from the insults and over-the-top statements that have gained himself so much press in the past year, as he needs to increase support outside his base.

With less than two months to go until November' s presidential election, Trump will have to stay on message and away from the temptation to hurl personal attacks and insults against rival Clinton during the nationally televised debate, experts said.

"He needs to stay on message that he is the agent of change and she (Clinton) represents the status quo. This is his best strength against her. He doesn't have to hit a home run, just to avoid a series of errors that undermine public confidence in his ability to do the job," Darrell West, vice president and director of governance studies of the Brookings Institution.

Clinton, however, will use Monday's debate as a chance to trip up Trump in hopes that he will engage in his typical name calling and insults. Many voters see Trump as temperamentally unfit to be president, and Clinton hopes to capitalize on this.

"Clinton's goal is to goad Trump into intemperate statements that make him look unfit for the presidency," West said.

If Clinton can get Trump to say outrageous things, it will remind people of his statements that and that he does not appear very presidential, West told Xinhua.

Trump in the past has compared Mexicans to rapists, called for a ban on Muslims entering the United States, and has made personal insults against political rivals.

Dan Mahaffee, an analyst with the Center for the Study of the Presidency and Congress, told Xinhua that Clinton has to draw Trump's "worse characteristics out."

But whether Trump can resist the temptation to spout off against Clinton on the debate stage remains unknown.

There have been past instances in which the very vocal candidate has seemed to tone it down, delivering serious policy speeches that are argued in a coherent way. But then just days later he would make an off-the-cuff remark that would erase all the gains he made.

Recent weeks have perhaps seen the longest stretch of time in which Trump has refrained from, essentially, being Trump. But it remains unknown whether he can keep it up, especially on the debate stage with Clinton.

For her part, Clinton's challenge is to present herself as more approachable and down-to-earth in a country where citizens want their leaders to understand the struggles of ordinary Americans.

"Her biggest challenge is relating to ordinary voters. People want to know that she cares about them and will undertake meaningful actions that will improve their lives. If she can do that, it will be a good night for her," West said.

Other experts said the debate is crucial for both candidates, as polls show that the two candidates have among the highest negative rates -- essentially the number of people who don' t like them -- in recent presidential history, polls show.

"In an election cycle where so many people have a negative viewpoint of both candidates, this debate is vital for both differentiating each candidate from their opponent, as well as ginning up the base," Mahaffee said.

While it may not be "make or break," it's vital for Trump to use this debate to further his momentum that's seen him close the gap with Clinton, he said.

Julian Zelizer, professor of history and public affairs at Princeton University, told Xinhua that it's not clear Trump wants to resist the temptation to throw personal insults at Clinton.

"I think he will allow some of that Trump to appear, balanced though with the more restrained figure that will be necessary for him to appear presidential," he said.