For the first time, Republican presidential front-runner Donald Trump has secured the endorsement of a sitting U.S. senator—Jeff Sessions of Alabama—a "biggie" as the billionaire calls him since Sessions sits on the Senate Judiciary Committee and is the chairman of the Senate sub-committee on Immigration, NBC News reported.

Sessions told a large crowd in Madison, Alabama on Sunday that he was throwing his support behind Trump because "at this time in America's history, we need to make America great again!"

The endorsement from Sessions is especially meaningful since in his nearly 20 years in Congress, the senator had never endorsed a presidential candidate.

Trump was visibly elated by the endorsement. "When I get Jeff Sessions, that means a lot to me. That means a lot. That's a biggie, especially since he's never done it before," he said.

Pundits say the endorsement will serve to bolster Trump's conservative credentials and further legitimise his plan to build a wall along the southern U.S. border and have Mexico foot the bill. This is because Sessions has long been working to fix illegal immigration. "Donald Trump will do it," he announced to cheers from the crowd.

The endorsement follows the show of support extended by a former Republican presidential rival, New Jersey Gov. Chris Christie. Virtually erasing all the criticisms he hurled on Trump before he ended his own campaign run, Christie said he is now fully behind the New York real estate mogul, who he said is a longtime friend.

In fact, Christie joined Trump on Friday and Saturday on the campaign trail, speaking highly of Trump's credentials and attacking his rivals, particularly Sen. Marco Rubio of Florida.

On Saturday, Trump also received the endorsement of former Arizona governor Jan Brewer, who in 2010 said that undocumented people bring into the U.S. "everything from the crime and to the drugs and the kidnappings and the extortion and the beheadings," Raw Story reported.

Trump said in a statement that he felt "honoured" to receive the endorsement from Brewer.

Overseas, Trump also received a vote of confidence from Jean-Marie Le Pen, the former leader of France's Front National.

"If I were American, I would vote Donald Trump," Le Pen tweeted on Saturday. "But may God protect him!"

Le Pen, who regularly offends racial and religious minorities with controversial comments, founded Front National, a far-right party that campaigns mostly on anti-immigration policies.

Marine Le Pen, Jean-Marie's daughter, currently leads the party, which expelled its founder last year for the extremity of his views.