Florida Gov. Charlie CristCharles (Charlie) Joseph CristHouse GOP secures last-minute change to gun bill On The Money: Shutdown Day 25 | Dems reject White House invite for talks | Leaders nix recess with no deal | McConnell blocks second House Dem funding bill | IRS workers called back for tax-filing season | Senate bucks Trump on Russia sanctions Democrats turn down White House invitation for shutdown talks MORE's (R) Senate bid received the endorsement of Sen. John McCainJohn Sidney McCainWhat should Democrats do next, after Mueller's report? Tom Daschle: McCain was a model to be emulated, not criticized Former astronaut running for Senate in Arizona returns money from paid speech in UAE MORE (R-Ariz.) on Wednesday.

You may recall that Crist's well-timed endorsement of McCain in last year's GOP presidential primary boosted the Arizona senator to a win in the Florida primary. McCain went on to win the GOP nomination.

In a statement, McCain stressed Crist's fiscally conservative credentials.

"Now more than ever, we need leaders who are committed to lower taxes, limiting government spending, and fighting for the people are needed in Washington," McCain said.

"I was proud to have had Charlie's support in my campaign, and I am proud to support him in his campaign," McCain added.

Crist, whose popularity ratings remain high, is considered the GOP's best shot at holding retiring Sen. Mel Martinez's (R) seat next year. Crist is facing a primary, though, against former Florida House Speaker Marco Rubio (R).

A poll released on Tuesday showed Crist with a commanding 53 percent to 18 percent lead over Rubio.

The winner of the GOP Senate primary will face either Rep. Kendrick Meek (D) or state Sen. Dan Gelber (D) in the general election.

The poll also found Crist hold significant leads over both Meek and Gelber.