Why can't Obama attack back?

From businessweek.com

Presumed Republican nominee Sen. John McCain, speaking in Pennsylvania, again advocated more oil drilling off the U.S. coast. 'Anybody who says that we can achieve energy independence without using and increasing these existing energy resources either doesn't have the experience to understand the challenge that we face or isn't giving the American people some straight talk,' he said.

Straight talk???!!

• Anyone who argues that we can solve our addiction to oil by drilling in the outer shelf is acting as a shill for the oil companies. Why can't Obama say that?
• Anyone who fails to point out that the oil companies are sitting on leases on which they can currently drill but are refusing to do so is acting as a shill for the oil companies. Why can't Obama say that?
• Anyone who fails to point out that Exxon/Mobile made Billions of dollars in profit in the last quarter alone and wants still more tax breaks is acting as a shill for the oil companies. Why can't Obama say that?
• Anyone who doesn't point out that the demand for drilling is simply a further land grab by the oil companies is acting as a shill for the oil companies. Why can't Obama say that?

This is what the Republicans always do. They make the contest into one in which Republicans attack Democrats and Democrats defend themselves. Why can't the Democrats attack back? Or perhaps Obama really doesn't have the substance to be President if he can't deal with this sort of tactic.