Rep. Joe Sestak is telling his supporters he will run for Senate in Pennsylvania in 2010 against freshly-minted Democratic incumbent Arlen Specter. The younger, more telegenic, more Democratic politician more beloved of the money-raising Netroots will soon be discussing his final decision with his immediate family, TPM reports.

Here is the text from a handwritten note to supporters:

"I am writing you as especially dear supporters to let you know I intend to run for the U.S. Senate...my candidacy's credibility will have much to do with my fundraising success by the 30 June FEC filing deadline at the end of this quarter. Would you help me bring the change for the future we Pennsylvanians need[?]"

Infantino confirms that the note is genuine and that "Joe Sestak has written a number of similar notes."

Daily Kos is already directing donors to Act Blue for the liberal former admiral. Sestak, who supports card check legislation for unions, has warned in th epast that unless Specter changes his tune on the Employee Free Choice Act, his labor support will be vulnerable.

Update: Pat Toomey on Sestak:

“While Joe Sestak and I disagree on a host of issues,” Mr. Toomey said, “I commend him for being a principled liberal who stands up for his beliefs and values. I have always believed that Pennsylvania voters—not party bosses in Washington—should have the final say over whom their nominees will be.”