(Newser) – While Mitt Romney and President Obama are busily downplaying tonight's debate, they're just as furiously preparing to spar live on stage at the University of Denver. On Sunday, Romney ran a full run-through of the 90-minute debate at an empty arena in Boston, with Rob Portman playing the role of Obama, reports the Wall Street Journal. Apparently the senator did a good job, since Romney said at times he wanted to kick Portman out of the room. "I will never debate Rob Portman again," Romney joked.

And while Obama has poked fun at Romney's intense preparation, he himself has been hunkered down in Las Vegas since Sunday honing his debate skills in front of an audience of advisers, with John Kerry channeling his inner Romney. "The president recognizes it as one of the biggest audience he'll have between now and November," says a spokeswoman. Click for what you need to know about tonight's debate.