In the few days since Mitt Romney swept the Wisconsin, Virginia and Washington, D.C., primaries, the Republican Party seems to have decided that it is, in fact, OK with the former Massachusetts governor as the GOP nominee.

As Romney counts his delegates and prepares for the final stretch of the primary season, the spotlight turns to just who hill pick as a potential running mate.

Senator Marco Rubio insists, just last week even, that he has no interest in the position. South Carolina Governor Nikki Haley told ABC News that if Mitt Romney called and offered her the nomination she would say, "No, thank you." New Jersey Governor Chris Christie has wavered, explaining to "Meet the Press" that, "I absolutely believe that, come November 2012, I’m going to be governor of New Jersey and not in any other office." But, Christie continued, "the fact of the matter is, if Governor Romney, who’s going to be our nominee, picked up the phone and called me to talk about this, I love my country enough and I love my party enough to listen."

Takeaway Washington correspondent Todd Zwillich said this is both a high-stakes decision, and one that could hardly matter.

"The public, I think, has a misconception about how much the vice presidential choice delivers in terms of electoral returns," Zwillich said. "However, there is no doubt a popular pick from a swing state can deliver that state. And in a close election, a state like Ohio, or Florida, delivered to your camp that would be on the razor's edge, could deliver the election."

But, speaking nationally, he said, it's hard to think of a time when a specific candidate really made a difference in the national popular vote.

"It's hard to imagine that. It doesn't really happen," Zwillich said.

But once in the White House, there decision can have impact far greater than it once did. Thanks, in no small part, to Dick Cheney.

"I think the era of the useless vice president is probably over," Zwillich said.

And there are several examples of times when a vice presidential selection was, in fact, a big deal. Look at Lyndon Johnson, who John F. Kennedy chose in order to win Texas but who was thrust into the White House upon Kennedy's death and oversaw a dramatic build-up of forces in Vietnam.

"Johnson turned out to be the most consequential vice president," Zwillich said. "He was extremely prepared. Highly effective, one of the most consequential vice presidents of the last 50 years."

But for every Johnson, there was a Dan Quayle, or a Spiro Agnew. Or even Sarah Palin, who never made it to office but made a major impact on the John McCain campaign.

"Sarah Palin ... in Washington right now is being discussed as the what-not-to-do for somebody like Romney. There were good reasons to choose somebody like Sarah Palin. She was unknown. She was charismatic. She was a compelling public speaker to a lot of people. She was very conservative," Zwillich said.

She was something of a hail mary pass, he said.

But because it didn't work so well last year, Zwillich said Republicans now are looking to avoid that dynamic.

So who's on the list? How about Christie, who is popular and could move a reliably-blue state (New Jersey) into the Romney column.

"People on the right are increasingly liking him. There's a lot that people like about him," Zwillich said. On the other hand, "he's gaffe-prone. He tends to make mistakes and he has a temper."

Zwillich put Christie at the "bottom of the top tier."

Then there's Haley — someone who could help Romney with his woman problem.

But Haley comes from a red state, so there's not likely to be any electoral bounce from her selection. That said, she's young and charismatic and popular with conservatives.

"Which might help Mitt Romney where he's weak, politically, which is with Tea Party folks and conservatives," Zwillich said.

Zwillich said even Rick Santorum, who is technically still challenging Romney for the nomination, has a great deal of support to be the vice presidential nominee — in part because of all of the delegates he's accumulated.

"The trouble is, Rick Santorum hasn't really been running for vice president. He's been tearing Romney to shreds," Zwillich said.

Then there's Paul Ryan, the outspoken conservative congressman from Wisconsin, the chairman of the House budget committee.

"Certainly seems to get along with Mitt Romney. They got along swimmingly up in Wisconsin — and that's not nothing," Zwillich said. "Mitt Romney notoriously does not have a lot of friends in the Republican Party. He may be able to win. He may be able to get support, but not a lot of like. They seem to like each other."

Rubio, who's been the most popular candidate all along, seems to be putting distance between himself and the nomination. It's hard to tell, though, whether that's sincere or an effort to reduce expectations, just in case he isn't asked.

Zwillich said one other name to keep in mind is U.S. Sen. Rob Portman of Ohio.

"He's a budget man, a former Bush budget official. A lot of people like Portman from that swing state of Ohio," he said.