The AARP officially endorsed the Senate health bill on Tuesday, giving Democrats a shot in the arm as they struggle to unite their caucus.

AARP CEO A. Barry Rand announced the group's support in a letter to Harry Reid, tying his group's support to Reid's pledge to close the Medicare "doughnut hole."

"With your commitment to closing the doughnut hole in conference, consistent with the president’s pledge, and the many positive features referenced above, AARP is pleased to support your efforts to obtain cloture, and urges timely passage of this legislation by the Senate," Rand wrote.

And here's a paragraph that Democrats will seize on in their attempts to beat back GOP arguments that the bill would drastically cut Medicare:

This bill will strengthen Medicare by eliminating cost barriers to preventive care, reform Medicare’s payment and delivery system to promote care coordination, and reduce hospital infections and preventable readmissions. Moreover, through critical insurance market reforms and the establishment of exchanges, this bill will give the uninsured and small businesses access to quality affordable plans. The legislation also includes important provisions to strengthen home and community-based care and to assist individuals in saving to meet future long-term care needs.

White House communications director Dan Pfeiffer touted the endorsement in a blog post.