Hillary Clinton could be facing her campaign's last gasp Wednesday night as she faces off against her Democratic rival in a marquee televised debate, as new polls and endorsements show more momentum swinging Barack Obama's way.

The two candidates meet for 90 minutes six days before Pennsylvania voters head to the polls in this must-win state for Clinton.

But new polls cast serious doubt on Clinton's ability to shore up the support she needs nationally to beat Obama, much less win a clear victory before the August Democratic National Convention.

A new Gallup Daily tracking poll of national Democratic voters shows Obama has posted his widest lead so far over Clinton in the poll. Obama claims 51 percent support to Clinton's 40 percent in the April 12-14 poll.

A Washington Post/ABC News poll shows more Democrats are questioning Clinton's trustworthiness -- even after a steadfast push over the weekend to try to paint Obama as an elitist and out of touch with Americans. The poll said a majority of Americans now believe Clinton is dishonest. She trails Obama among Democrats by 23 points on the question of honesty. While 63 percent of Democrats believe she is honest, that is 18 percent less than in 2006.

An Los Angeles Times/Bloomberg News poll shows that while Clinton still leads Obama in Pennsylvania and Indiana, her lead is not sufficient to wrap up the nomination. The poll of likely Democratic voters gives Clinton a 46 percent to 41 percent edge in Pennsylvania, and a similar 40 percent to 35 percent lead for Obama in Indiana. In North Carolina, Obama has a larger, 13- point advantage.

Separately, a Philadelphia Daily News/Franklin & Marshall College poll shows Obama inching ever closer to Clinton in Pennsylvania. After leading Obama 51 percent to 35 percent in March among likely Democratic voters, her lead had dwindled to 6 percent in the new poll: Clinton 46 percent, Obama 40 percent.

Clinton trails Obama 1,504 to 1,640 delegates. Pennsylvania has the largest number of delegates remaining to be selected for the convention. Delegates are apportioned according to a percentage of the vote.

Obama on Wednesday also added to his list of newspaper endorsements, taking that of Pennsylvania's capital paper, The Patriot-News in Harrisburg, as well as The Pittsburgh Post Gazette and the Bucks County Courier Times.

Both Clinton and Obama were holding morning events in the lead-up to Wednesday night's debate in Philadelphia. Obama was meeting with Jewish leaders in Philadelphia, and Clinton spoke at a building trades conference in Washington, D.C.

Ahead of that speech, Clinton did rack up another endorsement of her own on Wednesday, from the 45,000-strong Operative Plasterers' and Cement Masons' International Association.

The Post/ABC News poll also shows some bright spots for Clinton. For instance, the majority of Democrats polled -- 55 percent -- don't want her to drop out if she loses in Pennsylvania, and only 51 percent of Democrats and Democratic-leaning independents want Obama to face presumptive Republican nominee John McCain in the November general election. Clinton is preferred by 41 percent, though she loses to McCain by a few points in a hypothetical head-to-head match-up.

Democratic strategist Michael Brown warned against counting out Clinton too early.

"I think we have to discount the polls a little bit," he said. "There's a poll that has Hillary Clinton neck and neck or up five or six points in Florida against McCain. There's another poll that has Senator Obama down 20 points in Florida to John McCain so I don't know if polls should really make a difference. The bottom line is if she wins Pennsylvania, that shows that she continues to stay in the race and she has momentum."

But one Republican observer told FOX News he believed that the death knell is now ringing for the Clinton campaign.

" Put a fork in this campaign for Hillary. I think this is the last stand for her. I came to this position reluctantly. ... I think the groundsell among Democrat rank-and-file is such that they've settled on their horse, and that horse is obama," said Michael Steele, GOPAC chairman.

Click here to view the Gallup poll

Click here to view the L.A. Times/Bloomberg poll

Click here to view The Washington Post/ABC News poll