Romney's veepstakes heats up

(CBS News) WASHINGTON -- Republicans hold their national convention in less than three weeks. Only one major issue still needs to be decided: a running mate for Mitt Romney. The anticipation and speculation are growing fast. The big questions: When will Romney make his announcement - and who will it be?

In Iowa Wednesday, it looked and sounded like another day on the campaign trail for Mitt Romney. "This economy has been tough for a long time," he said at one stop.

But behind the politicking, Romney is weighing what some say will be his most important decision as a candidate: the running mate selection.

Romney's wife, Ann, added to the buzz Wednesday, tweeting, "Mitt's choice will be announced soon."

Earlier in the week, vice president watchers wondered if they'd gotten a clue.

Republicans started rolling out their convention speakers and several, including former Secretary of State Condoleezza Rice, had been rumored to be on Romney's short list.

With the prime VP speaking slot still open, some wondered if the announced speakers didn't make the cut.

Romney's potential picks

Romney quickly shut down the speculation, saying on Fox News, "The fact that someone is speaking at convention doesn't mean they might not find a speaking slot changed from one time to another."

Now the focus is on a bus tour Romney kicks off Saturday. He'll be joined by potential number twos: Ohio Sen. Rob Portman and, reportedly, Fla. Sen. Marco Rubio.

But if there's anything to learn from past VP reveals, it's to expect the unexpected.

Full coverage: Election 2012

Take 2008, when Sen. John McCain surprised the country by going with then-Alaska Gov. Sarah Palin.

"I think we hit the Richter scale on surprise," recalls Rick Davis, who was McCain's campaign chairman.

He helped convince McCain to select Palin, knowing he needed a game-changing pick.

But Davis says Romney doesn't need to be as bold, because the race already is close. "There's no question that he's in a little more enviable position than John McCain was," Davis says. ... I think he's a very conservative man. I think he will probably want someone who will be like him -- you know, someone who will govern with the same style and philosophy."

On Romney's short list: Portman and former Minn. Gov. Tim Pawlenty, considered "safe" picks, even though influential conservative writer Bill Kristol is encouraging Romney to "go for gold" by picking Paul Ryan or Rubio.

To see Jan Crawford's report, click on the video in the player above.