Presidential candidate Barack Obama said Friday the running mate he has chosen – but has not yet announced – had to meet three standards to join the Democratic ticket: Prepared to be president, able to help him govern and willing to challenge his thinking.

Those criteria did little to narrow the guessing game as Obama prepared for a massive rally in Illinois on Saturday to present his No. 2 to the nation and undertake a pre-convention tour of battleground states. He planned to disclose his choice through text messages to supporters, perhaps as early as Friday.

“Obviously, the most important question is: Is this person ready to be president?” Obama said in an interview aired Friday on “The Early Show” on CBS. Second, he said, was: “Can this person help me govern? Are they going to be an effective partner in creating the kind of economic opportunity here at home and guiding us through some dangerous waters internationally?”

And, he added: “I want somebody who is going to be able to challenge my thinking and not simply be a ‘yes person’ when it comes to policymaking.

One person who had been vetted for the position told The Associated Press there had been no contact from Obama or his campaign about the decision.

The Illinois senator was widely thought to be considering Virginia Gov. Tim Kaine, Gov. Kathleen Sebelius of Kansas and Sens. Joe Biden of Delaware and Evan Bayh of Indiana. None of them gave anything away – at least not in words.

Sebelius is at the Statehouse for a day of official business as speculation continued to swirl around her about being Barack Obama’s running mate.

When asked by reporters about Obama’s plans Friday morning, she again declined comment.

Sebelius has repeatedly referred questions about her chances of landing on the Democratic presidential ticket to Obama.

There has been plenty of speculation that Obama has narrowed it to four people, including Sebelius.

So far there has been no sign of increased security around Sebelius.

She spent much of Thursday in Iowa campaigning for Obama.

Sebelius aides said that on Friday, she will interview judicial candidates, meet with staff and prepare for the Democratic National Convention next week. She is also expected at an AFL/CIO meeting in Topeka.

She plans to take a commercial flight out of Kansas City to Denver on Saturday, aides said.

“I’ve made the selection, that’s all you’re gonna get,” Obama told The Associated Press.

Obama spent part of the day campaigning with Kaine, who reportedly told a colleague Wednesday that he believed he was on the short list. West Virginia Gov. Joe Manchin said Kaine told him although he hadn’t heard anything from the Obama campaign on where he stands at the time, “he really thinks he has a chance at the short straw.”

Kaine and Obama met privately with the governor’s staff for 15 minutes at a Richmond hotel. Afterward, Kaine said he would let the Obama campaign speak about whether the candidate asked him to be his No. 2. But two people close to Kaine said the governor was still in the dark.

Kaine plans to fly Friday night directly from Virginia to Denver, site of next week’s convention, three people with knowledge of the governor’s travel plans said. The plans could be changed if Kaine is told he needs to fly to Springfield, Ill., for the Saturday rally instead.

Biden had a family gathering at his home Thursday afternoon, with his wife Jill, niece Missy Owens and son Beau, Delaware’s attorney general, coming and going past reporters staked outside.

Bayh worked in his Capitol Hill office and later spent time at his home in Washington. He left wearing shorts and a baseball cap but told reporters outside he had no news to share. “Not tonight, sorry,” he said.

Two long-shots appeared out of the running.

Former Georgia Sen. Sam Nunn’s spokesman said he would be traveling internationally until Monday, making a Saturday visit to Illinois seem unlikely. And, Sen. Jack Reed of Rhode Island, a national security expert, told an AP reporter that he was not Obama’s choice and that he had not been asked for any background information.