The spotlight Thursday belongs to the "number twos." The candidates for vice president will square off in their one-and-only debate, and experts said there's a lot on the line for both men.

Republican presidential hopeful Mitt Romney has been steadily gaining in the polls since President Barrack Obama's performance in last week's presidential debate. 

Political pundits said that's exactly why Thursday's showdown of the V.P. candidates is so important.

Vice presidential debates are rarely a critical event in White House campaigns, but the stakes are high this year.

John Kincaid, a professor of government and public service at Lafayette College in Easton, said both candidates are feeling the pressure.

"Ryan needs to maintain the Romney bump and not damage that, and Biden really needs to give Obama a bit of a bump," said Kincaid.

But according to Kincaid, Biden has the most hanging in the balance.

"There's going to be even more pressure on Joe Biden because Obama did so poorly on the first debate," explained Kincaid.  "Biden has to start pulling it out from that."

The likely outcome will be a debate filled with attacks and counter attacks.  Kincaid said if Biden is clearly stomped by Ryan, the Republican momentum will continue to build.

"I think if he loses the debate, that will be a major problem for the Democratic campaign," he said.  "That will put a lot of pressure on Obama to have to rescue it in the rest of his campaign and the other debates."

So, we may see Biden more confrontational, trying to discredit the Republicans.  Experts said one clear benefit for Biden is his debate experience over Ryan.

"Ryan is not used to being on the national stage," said Kincaid.  "His debates have been more local as a member of the house."

The debate will begin at 9 p.m.