Evangelical Christians might cost Republican nominee Donald Trump his shot at the White House, according to conservative Rep. Steve King.

"Mitt Romney left five to eight million evangelical Christians home in 2012 or he'd be running for re-election right now, by some analyses," the Iowa republican told "Morning Joe" on Monday. "I think that's an important message to say to the conservatives: Staying home is going to give you more of what you have today and probably worse of what you have today under Barack Obama."

Low GOP voter turnout has been a fear in Republican circles for months. A survey conducted in March by an anti-Trump group showed that 40 percent of evangelicals and 40 percent of self-identified conservatives viewed him negatively, and weekly church attendance was the best predictor of Trump opposition during the primaries.

King's warning also was an extension of Texas Sen. Ted Cruz's stated campaign strategy of turning out more conservatives than in 2012. "Imagine instead millions of people of faith all across America coming out to the polls and voting our values," Cruz said throughout the campaign.

Cruz's speech at the Republican National Convention in which he told convention-goers to "vote your conscience" exacerbated concerns about GOP turnout when the remarks were interpreted as the senator authorizing his backers to consider refusing to back Trump. But King, who endorsed Cruz in the primaries, suggested that's not happening in his district.

"The Republicans that are there — the people that were, many of them, that were strong Cruz supporters — are now stepping up and saying we've got to get Trump elected, we can't let Hillary win," he said.