WASHINGTON (CNN) -- Three national polls of Democrats show Sen. Barack Obama is the front-runner for the nomination. But what's behind this latest momentum?

New national polls show Sen. Barack Obama, right, trumping Sen. John McCain in November.

There's growing evidence that Obama is seen as more electable than Sen. Hillary Clinton.

If you average the "poll of polls" -- AP-IPSOS, USA Today/Gallup and CBS/New York Times -- Obama leads Clinton 50 percent to 40 percent, with 10 percent unsure.

Here's something Democrats agree on even more: In two different polls, around 70 percent of Democrats polled believe Obama will get their party's nomination.

When Democrats were asked about the general election, the New York Times-CBS News poll showed Obama had the best chance of beating Sen. John McCain -- 59 percent to Clinton's 28 percent.

And it's not just Democrats.

The USA Today-Gallup poll asked Republicans which Democrat would McCain have a better chance of beating.

The answer: Clinton 66 percent, Obama 18 percent.

Republicans are just itching to run against her. Her response? She's heard it all before.

"I hear all these folks talking about who is or isn't electable. Well, they said the same thing about me when I started running in New York. ... You know, nobody would vote for me, good grief. I was wasting my time and my money," Clinton recently said. "But I trust the voters, and frankly that's who matters."

All three national polls asked voters the electability question in a general election matchup.

They show Clinton in a dead heat with McCain -- both coming in with 46 percent.

Obama, meanwhile, leads McCain by seven points -- 49 to 42 percent.

So why does Obama do better? Here's his answer:

"It's a choice between going into the general election with Republicans and independents already united against us, or running with a campaign that has already united Americans of all parties around the agenda for change. Now that's the choice," Obama has said.

Independents are crucial swing voters. They give McCain a solid lead over Clinton, according to the New York Times-CBS News poll. But independents abandon McCain for Obama.

If Obama's the alternative, McCain's support among independents drops from 52 percent to 36 percent.

The difference in electability looks small, and neither Democrat looks like a sure winner or a sure loser.

But the belief that Obama is more electable is taking hold.

The national "poll of polls" consists of three surveys: AP-IPSOS (February 22-24), USA Today/Gallup (February 21-24), and CBS/NYTimes (February 20-24). E-mail to a friend

All About Barack Obama • Hillary Clinton • U.S. Presidential Election • John McCain