Sen. Lamar Alexander (Tenn.), one of the top Senate Republicans, has endorsed former Massachusetts governor Mitt Romney for president.

Sen. Lamar Alexander (R-Tenn.) (AP)

Alexander made the announcement to reporters Friday during early-voting in Tennessee’s Blount County, according to the Romney campaign.

The move lends Romney the backing of an influential two-term senator and former GOP presidential hopeful who until last month served as the No. 3-ranking Senate Republican. (Alexander voluntarily stepped down from the post, announcing in September, “What I’m giving up is a seat at the table for more independence.”)

“I learned a long time ago that Tennesseans didn’t elect me to tell them how to vote, but I voted for Governor Romney,” Alexander told reporters in Tennessee Friday afternoon, according to the Romney camp. “We’re electing a commander in chief who knows something about creating jobs, not a legislator in chief. For me, Governor Romney is the right choice.”

Alexander cited Romney’s executive experience and his ability to attract independents as among the reasons he decided to back the former Massachusetts governor.

Romney’s Capitol Hill endorsement list now stands at 79, according to a tally maintained by Roll Call. Former Pennsylvania senator Rick Santorum has garnered four, including Rep. Bob Aderholt (R-Ala.), who endorsed him Friday morning.

Democrats were quick to point out that the endorsement by Alexander – who in 2009 was the first Republican to support the confirmation of Supreme Court Justice Sonia Sotomayor – comes as Romney’s camp is up with a new Michigan TV ad slamming Santorum for, you guessed it, backing “liberal Judge Sotomayor.”