Obama general counsel Bob Bauer today sent a second, sharper letter to the Justice Department, directly attacking the Dallas billionaire funding a harsh attack ad, Harold Simmons.

“We reiterate our request that the Department of Justice fulfill its commitment to take prompt action to investigate and to prosecute the American issues Project, and we further request that the Department of Justice investigate and prosecute Howard (sic) Simmons for a knowing and willful violation of the individual aggregate contribution limits,” he wrote.

He called the group’s activities “patently illegal.”

Bauer made the case that Simmons’ group fulfilling its a real nonprofit charter because it hasn’t spent any money on anything other than attacking Obama.

The American Issues Project released a statement responding to the letter.

“Having failed in its attempts to get our legal, factual and fully-supported ad off the air, Barack Obama’s campaign now wants to put our donors in prison for exercising their right to free speech,” said Ed Martin, the group’s president. “These over-the-top bullying tactics are reminiscent of the kind of censorship one would see in a Stalinist dictatorship, with the only difference being that those guys generally had to wait until they were in power to throw people who disagreed with them into jail.”

The group said its ad would continue to air through the end of the Democratic National Convention. Simmons has spent almost $3 million to air the ad, which can be seen on the group’s site. (Here is the ad)