The White House on Tuesday expressed optimism about the Democrats' chances of holding the open Senate seat in Pennsylvania on the heels of two polls showing their candidate taking the lead.

President Obama's top politcal adviser in the White House, David Axelrod, appeared confident during an interview on CNN that Rep. Joe Sestak (D-Pa.) could defeat his Republican opponent, former Rep. Pat Toomey, who leads the race in most polls.

"But I think that you'll see, all across the country, Democrats winning in places that, you know, were written off. And just today we saw a poll in Pennsylvania where Joe Sestak had been trailing and is now — is now marginally ahead in that race," he said. "I think that momentum has shifted in that race."

Republicans have identified the Pennsylvania race as a key pick-up opportunity in their quest to take control of the Senate this cycle. 

Most polls show Toomey with a single-digit lead over Sestak, but two surveys released this week showed Sestak taking the lead. But a poll released Monday by Democratic firm Public Policy Polling showed Sestak narrowly leading Toomey, 45 percent to 44, and an independent poll commissioned by the Morning Call showed the Democrat leading the Republican by three percentage points, 44-41, with 15 percent undecided.

Axelrod went as far as to call the race a potential "harbinger" of the results for Democrats countrywide.

"So it's a competitive — it's a competitive race here," he said. "But I am going to be looking at that race in — in Pennsylvania as a, you know, as an East Coast harbinger of the kind of night it's going to be."

Toomey spokeswoman Nachama Soloveichik denied any momentum swing to Sestak's side.

“The polls are all over the place, with most of them showing a good sized lead for Pat Toomey," she said in an e-mail. "But the bottom line for Pennsylvania voters is a clear choice between more of the same reckless Washington spending and high unemployment with Joe Sestak, or a change in direction toward fiscal discipline and job growth with Pat Toomey."

The seat had been held by Sen. Arlen Specter, a longtime Republican who switched parties last year, in part to avoid a primary rematch with Toomey, whom he defeated in the 2004 GOP primary.

But Specter, who earned the support of the White House, was defeated in the Democratic primary by Sestak, a second-term congressman and former Navy admiral. 

Tensions between Sestak and Obama ran high several months ago, when the candidate accused the White House of offering him a job to get out of the race against Specter. The GOP pounced on the accusation as an example of possible illegal conduct, but the president denied that anything improper took place, and the White House counsel released a document to that effect.

This post was updated at 10:27 a.m.