Feeling the pressure of an expected blockbuster 2010 GOP primary, Sen. Arlen Specter penned a letter to former Rep. Pat Toomey last week asking him to release his organization’s donor records.

Toomey, who came within 17,000 votes of defeating Specter in the 2004 GOP primary, has not officially entered the race but is expected to do so at any time. Toomey, who now heads the conservative, anti-tax Club for Growth, led Specter in recent polling, 41 percent to 28 percent.

Specter penned a letter to Toomey asking him to release a list of Club for Growth donors who received Troubled Asset Relief Program money. The letter, which was released to the media by Specter’s campaign, asked Toomey to deliver the results to him by April 13.

“In recent weeks as you have shifted your attention from a long-planned run for Governor to another Senate campaign, you have criticized the TARP bill I voted for last fall,— Specter wrote. “Given the Wall Street background of your members, it seems clear that many of them would have received TARP monies.—

Specter also hit the TV airwaves last week, becoming the first Senator to go up with ads in the 2010 cycle. According to Specter campaign manager Christopher Nicholas, the TV ads began running on cable stations across the state Thursday and the total cost of the buy is $100,000.

“Pat Toomey, as a Wall Street trader, he sold risky derivatives called credit default swaps — the same swaps that have plunged us into this financial mess,— the TV ad’s announcer says. “In Congress, Toomey fought for less oversight of Wall Street. He even wants to gamble our Social Security accounts in the stock market. Now Toomey wants a bonus: a seat in the United States Senate. Should we let him have it?—

Toomey responded to Specter’s ad in a statement by saying he never sold credit default swaps when he worked in banking.

“This is a desperate and silly attempt by Senator Specter to change the subject away from his support for Wall Street bailouts and massive new spending and debt in Washington,— Toomey said.