Cruz somehow reinvented himself (not altogether convincingly) as the most virtuous and Christian candidate in the race. While he has moved around the circles of power and initially attempted his assent by working through the establishment, he switched gears with the Tea Party wave and obtained his Senate seat through an explicit appeal to evangelicals, casting himself as a virtuous outsider in a world of corruption. He has, through personality traits and tactics, largely alienated his Senate colleagues, and he represents another wing of the anti-establishment vibe of this GOP presidential race. But his appeal to evangelicals and others is fragile to these adultery rumors, and I would suggest his performance above makes him appear guilty as hell. (One of the biggest signs of deception is (a) refusing to deny the accusation and (b) obfuscating through counter-accusations.)
Some have suggested this dirt came from Trump–who plays hardball no doubt–but I note this story appears originally to have come from the Rubio camp, and my expectation is that it sat on the sidelines as long as he was in the race because there is a meta-strategy by the GOP establishment not to help Trump, so Cruz and Rubio combined had more force than Cruz or Rubio alone. Now that Rubio is gone, someone with an axe to grind got this to the National Enquirer, and here we are. It does matter if it’s true, particularly to Cruz’s supporters, because his alleged virtue is the raison d’etre of his campaign and the keystone of his message. Trump, by contrast, is anti-fragile to the usual attacks because he does not claim to be Mr. Virtue, his Christianity is toned down and nominal (like many Americans today, incidentally), and his whole schtick is that he does not play by the usual rules and is politically incorrect.
I would add I think it’s pretty basic that if you are the type that wants to screw around, it may behoove you not to run for President. Everything comes out, whereas Senators and Congressman seem able to wallow in filth indefinitely.