The Politico's Mike Allen is reporting today that on Aug. 29, the day after Obama accepts the nomination as well as McCain's 72nd birthday, McCain will announce his VP. If accurate, this confirms what we posted yesterday from PolitickerOH that McCain was planning a huge rally in Ohio that day.

From Allen's story:

Senior Republicans are in the dark about who he'll name, although they say former Massachusetts Gov. Mitt Romney and Minnesota Gov. Tim Pawlenty are prime contenders after a trial balloon by McCain gave him very negative feedback about the idea of picking an abortion-rights running mate such as Tom Ridge, the former governor of Pennsylvania and the first secretary of homeland security.

Sources close to McCain say he has wrestled with the choice, torn between a high-stakes, high-reward pick like Ridge or Connecticut Sen. Joseph I. Lieberman -- the Democratic vice presidential nominee in 2000 -- or a safer and more conventional selection such as Romney or Pawlenty.

Friends say he has yet to make a final decision, and is not expected to do so until after Sen. Barack Obama announces his choice.

So although McCain knows when he'll announce, he doesn't know whom he'll announce. Which is just fine actually. After rumors that McCain was going to make a preemptive announcement while Obama was in Europe, the campaign seems to have settled down some and decided on the right course of action here: Wait. Let's see what cards Obama is going to show before making a decision.

The only downside of knowing that McCain will make the announcement on Aug. 29 is that it takes away a bit of the surprise factor. Unless McCain makes a big splash with his choice -- say, a Bobby Jindal, Sarah Palin or Joe Lieberman -- it could be considered a letdown. Which presents the campaign with a challenge to turn the event into something really big.