Another major Republican player is making a big bet that Mitt Romney has a chance at winning Pennsylvania.
Americans for Prosperity, the conservative advocacy group that is backed by the Koch brothers, will spend $1.5 million to run commercials criticizing President Obama there.
Pennsylvania has suddenly become a hotbed of action in the presidential race, after appearing largely out of play for the last few months.
But with polls showing Mr. Romney closing in on the president's lead there, Republican groups have rushed to get on the air and forced the Obama campaign to spend more it they had hoped to defend its position.
Restore Our Future and Americans for Job Security, two super PACs backing Mr. Romney, and the Republican Jewish Coalition are all spending large sums of money to advertise there.
Their moves prompted the Obama campaign to announce on Monday that it would shift resources to the state. As of Tuesday afternoon, the campaign had r eserved about $1.1 million in commercial time.
The new Americans for Prosperity campaign will add even more pressure on the president.
“The president likes to say, ‘Look at the math,'†said Tim Phillips, the group's president. “Well, when you look at the math in Pennsylvania, it's dangerous for the president.â€
Mr. Phillips said Republicans believe the president's standing among women is particularly vulnerable now, and that much of his group's advertising effort will be aimed at reaching undecided women in the Philadelphia suburbs.
The group will run two ads. One features former supporters of the president's who explain why they have since changed their minds. The other features a Canadian woman who says that her country's government-run health care system prevented her from receiving valuable treatment.
Americans for Prosperity will also spend another $1.5 million advertising in Michigan.
