Joey Garrison, and Dave Boucher

The Tennessean

Tennessee Gov. Bill Haslam has endorsed Marco Rubio in the Republican presidential primary, headlining the state's mounting GOP establishment support for the U.S. senator from Florida amid the rise of frontrunner Donald Trump.

Haslam and the Rubio campaign announced the endorsement Thursday morning, capping what had been days of speculation on whether the two-term governor would endorse Rubio.

“To win in November, conservatives need a candidate who inspires Americans from all backgrounds,” Haslam said in a statement. “With Marco standing next to Hillary Clinton on a debate stage, the choice between the future and the past will be clear to every American.

“Marco has the innovative policy agenda to reclaim the American Dream for all our people, and his conservative ideas will bring the Republican Party — and America — into the future.”

Former U.S. Senate Majority Leader Bill Frist, R-Tenn., also announced Thursday that he is now backing Rubio.

Frist, who had backed former Florida Gov. Jeb Bush, said in a statement that Rubio is ready to be "commander-in-chief."

"Marco also understands that it takes more than angry rhetoric to be an effective candidate for president," Frist said. "If the Republican Party wants to win back the White House, we need a candidate like Marco Rubio that can appeal to all types of voters.

"This is an important election with too much at stake to nominate somebody that cannot win the general election. If we nominate Marco Rubio, we will win in November and get America back on the right track."

It is unclear whether Tennessee U.S. Sens. Lamar Alexander and Bob Corker — both political allies of the governor — will join Haslam and endorse ahead of next week’s Super Tuesday primary in Tennessee. Corker told Roll Call this week he didn't plan to make any endorsements. Alexander has said the same thing, although a spokeswoman didn't immediately respond to a request for comment on Thursday.

Early voting in Tennessee ended two days ago ahead of election day on Tuesday.

The Associated Press first reported Haslam’s endorsement, which is the subject of a new Rubio campaign television advertisement that features Haslam speaking.

Many with close Haslam ties — including current Economic and Community Development Commissioner Randy Boyd and former ECD Commissioner Bill Hagerty — had been members of the Tennessee leadership team for Bush.

When Bush dropped out of the race after his loss in Saturday’s South Carolina primary, pressure started to build for Haslam — as well as Alexander and Corker — to get behind Rubio, who has quickly garnered backing from mainstream Republicans nationally to counter the surging Trump.

Trump has carried three consecutive states in the nomination process and he's polling ahead in most states that vote on Super Tuesday. That includes Tennessee where the most recent poll taken last month had him ahead of U.S. Sen. Ted Cruz by 16 percentage points.

Hillary Clinton to campaign in Nashville on Sunday

Rubio has lagged far behind both Trump and Cruz in those same Tennessee polls, but more than 3,500 people came to Franklin on Sunday to hear him speak, making it the largest crowd for a rally for Rubio up to that point.

Tennessee has 58 delegates up for grabs on Tuesday, the third-most of any of the 12 states that hold Republican primaries.

A record number of people voted early during this year’s presidential primary in Tennessee, with two-thirds of the 385,653 Tennessee voters casting ballots in the Republican primary.

Earlier this week, Haslam hinted that an endorsement from him was coming, though he stopped short of naming a candidate. He was coy, saying he’s “having conversations with those running for office as well as other people around the country.”

Tennessee’s last two Republican primary winners were former Arkansas Gov. Mike Huckabee in 2008 and U.S. Sen. Rick Santorum in 2012. Both benefited from strong support from evangelical Christians and weren’t the top picks of establishment Republicans.

Four years ago, Haslam endorsed Massachusetts Gov. Mitt Romney, who finished second in the Tennessee primary.

Reach Joey Garrison at 615-259-8236 and on Twitter @joeygarrison. The Associated Press contributed to this report.

Bill Haslam nearing presidential endorsement

'Feel the Bern' Nashville rally won't include Bernie Sanders