Mitchell McKinney, a professor of political communication at the University of Missouri, speculated that recent comments from Trump are being made with the thought that, “as we’re heading into Iowa, I’ll give the Cruz supporters something to doubt; maybe something to second-guess their choice.”…

But by Thursday, the senator’s wife, Heidi, was taking a more serious tack, insisting her husband is “indisputably a U.S. citizen.” Cruz himself, in an interview with Bloomberg, insisted that “the legal question is straightforward and clear” regarding his eligibility…

Trump’s new tone is still not as sharp as some people expected, however, given how serious a threat they believe Cruz poses for his candidacy.

“It’s puzzling why Trump is not going after Cruz more directly, because Cruz is a bigger threat than Trump thinks he is,” said GOP strategist Matt Mackowiak. “If Trump loses Iowa by a significant margin and then somehow loses New Hampshire … I think the whole thing falls apart. The piercing of that invincibility begins in Iowa.”