"Donald Trump has effectively secured the Republican nomination for president, and it is time for Republicans to support Donald Trump's candidacy," Burgum said in a statement Thursday May 5. "He has brought a record number of new voters into the Republican primary process, and we must now begin to grow that base by uniting our party's diverse coalitions. With the presidential nomination process effectively over, Republicans must begin focusing on winning the White House. The stakes this November are too high to wait. It is essential for North Dakota's economy that the next president be a Republican."

Burgum, who doesn't have his party's support in his run for the state's top executive job, has portrayed himself as an outsider fighting against the establishment. Trump, too, has portrayed himself as an outsider fighting the establishment. Both have touted their success as businessmen.

"Voters are looking for a political outsider because the status quo isn't working for many Americans," Burgum said of Trump. He has made similar arguments for himself in his ads. "We need business leaders in office that understand the changing economy."

Burgum said in his statement that "Americans will have two very different choices - Donald Trump or Hillary Clinton."

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Two other North Dakota Republicans, Sen. John Hoeven and Gov. Jack Dalrymple, who is not running for re-election, also said Thursday they would support Trump. But both Hoeven and Dalrymple stopped short of endorsing Trump, saying only that they'd support him as the party's nominee for president. Rep. Kevin Cramer, R-N.D., endorsed Trump last month.