Rep. Joe Sestak (D) announced he raised more than $1 million in the second quarter and that he ended June with more than $4.2 million in cash on hand as he prepares for a bloody primary battle with Sen. Arlen Specter (D) next year.

Sestak has yet to officially announce he is running against Specter, who declared earlier this year that he would switch parties to run for re-election as a Democrat in 2010.

In other Keystone State fundraising news, former Rep. Pat Toomey, who appears to be the odds-on favorite to become the Republican Senate nominee, announced he has raised $1.6 million for his campaign since April 15. Toomey ended June with $1.1 million in the bank.

Meanwhile, Sestak and Specter continued to assault each over via e-mail on Monday.

In e-mail to supporters, Sestak thanked his donors for “making us the number one Senate challenger in the nation!— and then lit into Specter for recently calling the Congressman a “flagrant hypocrite.—

“Arlen has decided his only shot at winning in the primary is to run a negative campaign’ against me; hence his attack on my military service and integrity,— Sestak wrote.

But Specter only continued to blast Sestak for his voting record in Delaware County — citing local records that showed the two-term Congressman only voted in 13 of the 35 general elections from 1971 to 2005 and only registered as a Democrat in 2006.

“So, how can Sestak claim to be a non-partisan Independent and the real Democrat— at the same time?— Specter wrote in a Monday e-mail.