Mitt Romney is skipping the next Republican debate, which will be held in Las Vegas in July. The next debate he plans to attend will be in August. Romney's Republican opponents will likely be more aggressive in criticizing him in future debates. Below is a good summary of the risks of skipping the debate from Daily Kos:

<< You may recall that Hillary Clinton enjoyed a healthy lead over her opponents at this point in 2007, and she, like Romney, pursued a front-runner strategy, avoiding conflict and trying to run out the clock. But what ended up happening is that when she finally faced attacks from her rivals, she was unable to recover before it was too late.

<< By any objective measure, Mitt Romney is the frontrunner, but yet we still don't know if he has a glass jaw. If he does, waiting until the fall to let his opponents take punches may prove to be a terrible decision, because it won't give him enough time to put things back together again. >>

Source:
http://www.dailykos.com/story/2011/06/22/987577/-Romney-to-skip-July-debate,-but-commits-to-six-others-through-October