Donald Trump scored his biggest coup yet by receiving the endorsement of Alabama Senator Jeff Sessions, a respected voice on immigration and trade.

Washington Examiner:

Sessions becomes the first Senate Republican to endorse Trump for president. Sessions cited immigration and trade, as his rationale for supporting Trump.

"I told Donald Trump this isn't a campaign," Sessions said. "This is a movement."

"Look at what's happening," Sessions said, referring to the size of the crowd. Trump claimed the crowd size was 30,000 people with 3,000 people still waiting to get in.

"The American people have known for years that these trade agreements have not be working for them," Sessions said. "We will soon have a vote on the Trans Pacific Partnership, Obamatrade. It will damage America."

"Donald Trump, when he gets elected president, will see that it does not pass," Sessions said.

"The American people are not happy with their government," Sessions said. "Some say 'You know, you just need to let the people calm down a little bit, and they'll forget it, and let it all go.' Should we forget it? No, we should not."

Meanwhile, Nebraska senator Ben Sasse became the first of what is expected to be a handful of GOP senators who will refuse to back Donald Trump as the GOP nominee.

Sen. Ben Sasse, a Nebraska Republican, said Sunday that he is unlikely to support real estate developer Donald Trump in a general election.

"If Trump becomes the Republican nominee my expectation is that I'll look for some 3rd candidate — a conservative option, a Constitutionalist," Sasse tweeted Sunday night.

Sasse, a conservative former university president, has previously been sharply critical of Trump's views, arguing the former reality television star does not embrace the conservative principles of limited government and liberty.

Sasse becomes the most prominent congressional Republican to announce plans to deny Trump his support.

"Christians — recognizing threats vs religious liberty — are unwilling to support candidate who doesnt offer full-throated defense" of the First Amendment, Sasse added.

"A presidential candidate who boasts of what he'll do during his 'reign' & refuses to condemn the KKK cannot lead the conservative movement," Sasse said.

During a Sunday appearance on NBC's "Meet the Press," Trump declined to denounce the white supremacist Ku Klux Klan.

Some observers believe there will be a tidal wave of senators who, like Sasse, will announce they cannot support the nominee in the general election.  I'd be very surprised if the number reaches half a dozen.  There are 24 GOP senators running for re-election who can't afford to alienate Trump voters.  There are another eight Republicans running in 2018 who figure it would be suicidal to oppose Trump.

The bottom line is that it's just not good politics to throw your presidential nominee under the bus.  I suspect that most senators who feel like Sasse will keep their opposition to themselves.

Meanwhile, the Sessions endorsement is a major victory for Trump.  It was believed that Sessions would end up supporting Ted Cruz, but it was Trump whose victories in the early primaries probably convinced him to go with the winner.

Sessions is well respected in Alabama, but according to the polls, Trump doesn't need his support.  He's winning by double digits in the state, as he is in most other Super Tuesday contests.