PITTSBURGH — It’s 3 a.m. and that darn phone is ringing again.

This time, it’s an economic crisis, not a national security issue.

And the person who can’t deal with it is not Barack Obama, who in the prequel was unable to deal with the security issue, but John McCain.

Yes, it’s the new ad from Senator Hillary Clinton.

Here’s the key line from the script of the 30-second spot, which is running statewide in Pennsylvania.

“John McCain just said the government shouldn’t take any real action on the housing crisis, he’d let the phone keep ringing,” the announcer says. “Hillary Clinton has a plan to protect our homes, create jobs.”

The interesting thing, of course, is why the Clinton campaign, mired in a Democratic contest with Mr. Obama, is spending money to go after the presumptive Republican nominee. Could it be that the Clinton camp and the Obama camp have reached an understanding that further fire at each other will only damage the party? Is there a temporary cease-fire while they work out the status of delegates from Michigan and Florida?

In a relatively mild conference call with reporters, Clinton strategists focused on Mr. McCain. They seemed to overlook the contest with Mr. Obama and avoided taking their usual pot-shots at him. They said that the ad is meant to show that Mrs. Clinton is more prepared to improve the economy than Mr. McCain, which in turn bolsters her argument that she can win in November.

“We think Democratic primary voters will rally around her,” Mark Penn, her top strategist and pollster, said.

Howard Wolfson, her spokesman, took exception to a suggestion that the ad, which uses recycled images, was an attempt to save money, though he acknowledged that the Obama campaign was likely to outspend them at least three-to-one in Pennsylvania.

“That is patently ridiculous,” Mr. Wolfson said. “The idea is to build on an ad that was extremely successful, that people will remember and that will have resonance in the context of the 3 a.m. theme.”

Don’t rule out hearing that phone ring a third time.

In response, the McCain campaign did not take it seriously. Steven Schmidt, a senior adviser to Mr. McCain, said that the only call Mrs. Clinton would be taking at 3 a.m. was one telling her that she had lost another superdelegate.

Related: On Line: Clinton’s Persistence Could Help Obama

Update| 7:15 p.m. : John McCain is releasing a response ad.

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