Republican presidential candidate, Sen. Ted Cruz, R-Texas, looks downward while listening to a question from the crowd at a campaign event at Bridge View Center, Jan. 26, 2016, in Ottumwa, Ia. 
Photo by Jae C. Hong/AP

Trump went ‘birther’ on Cruz because it works

As recently as mid-December, there was ample evidence that Ted Cruz had not only caught up to Donald Trump in Iowa, but the Texas Republican was actually in a commanding position. Polls showed Cruz surging; prediction markets found Cruz passing Marco Rubio in the overall race; and there were plenty of reports that the first presidential nominating contest was “Cruz’s to lose.”
Those headlines have since evaporated. Highlighting the Trump campaign’s latest “birther” attack on Cruz – the senator was born to an American mother on Canadian soil – The New Republic’s Brian Beutler raised an important point yesterday.
[T]aking stock of where we are, four days before the Iowa caucuses, it’s worth considering whether Trump is doing this for sport, or because it’s actually an effective line of attack. The evidence is striking. 
On January 6, 2016, the conservative Independent Journal Review published an article headlined “Trump Launches New ‘Birther’ Attack on Ted Cruz.”
Right, and almost immediately thereafter, Cruz’s fortunes reversed course. Take a look at the image on this page and note the exact date of the Texan’s peak poll position: January 7. When were reports first published on Trump attacking Cruz over his eligibility? January 6.
Note, Rubio’s been hammering related nonsense, too, but as is usually the case, the senator was a follower, not a leader – Trump got this started; Rubio just opportunistically jumped aboard.
But it’s hard not to note the timing: Cruz’s slip in the polls just happened to coincide perfectly with the line of attack on Cruz’s Canadian birthplace.
Indeed, there’s some quantitative evidence to consider. Public Policy Polling released this report yesterday afternoon:
Cruz has seen a large drop in his favorability rating over the last few weeks, from 69/18 down to just 56/35. Trump’s continued focus on the ‘Canadian birther’ issue may really be a big part of what’s helping him at Cruz’s expense. We found on our last Iowa poll that only 32% of Republican voters thought someone born in another country should be allowed to serve as President, and attention to Cruz’s birthplace has been a constant since that last poll.
My sense is that when Trump (and later Rubio) first started emphasizing Cruz’s Canadian roots, pundits and mainstream political observers were inclined to just shrug it off. That was, of course, the appropriate reaction – this line of attack is absurd. I can think of all kinds of reasons to be concerned about Cruz’s candidacy, but his eligibility for the office is not in doubt.
Indeed, for many, it seemed literally laughable. The senator’s campaign initially responded to the offensive by tweeting the infamous “jump the shark” scene from “Happy Days.”
But just because mainstream political observers dismissed it as silly doesn’t mean Republican voters were equally unmoved. There’s circumstantial evidence pointing in a very specific direction.