The progressive groups whose ad against Sen. Ben Nelson (D-NE) caused him to lash out last week have tripled their ad buy against him, reports Greg Sargent.

As we reported Friday, Nelson responded to the ad by releasing a statement that said, in part, "If this is an indication of the politics going into August, then health care reform may be dead by the end of August."

In other words, shut up or we'll kill health care reform.

Here's part of the email sent out today by the groups, Progressive Change Campaign Committee and Democracy For America:

Well, we're not playing that game, Senator. That's not how a democracy works. And bold progressives don't cave to intimidation from corporate Democrats.

So today, with our partners at Democracy for America, we're tripling our ad buy in Nebraska and doubling it in DC.