Keep the Promise, the network of super PACs supporting Sen. Ted Cruz (R-Tex.) for president, is starting the final week before the Iowa caucuses with new attacks on Donald Trump. One makes use of the 1999 interview Trump gave the late Tim Russert, which Cruz has cited frequently to argue that the front-runner's "New York values" make him a phony conservative.

In the clip, a more youthful Trump pronounces himself "very pro-choice in every respect." He repeats that when asked about "partial-birth abortion," a late-term procedure that would be banned by a Republican president and Congress four years later.

Keep the Promise, a group of super PACs supporting Sen. Ted Cruz (R-Tex.) for president released an ad that features a 1999 clip of Republican presidential candidate Donald Trump saying, "I am very pro-choice." (YouTube/Keep the Promise)

This ad, alongside a previously-released found-footage spot in which Trump praises Cruz, will be part of Keep the Promises's ongoing $2.5 million buy in Iowa and South Carolina. Since ending his detente with Trump, Cruz has repeatedly asked voters to consider the 1999 interview. "He explained in his views that he was pro-choice, he supported partial-birth abortion, was open to gay marriage, and his explanation for all that, he said, I’m a New Yorker, I’m from Manhattan," said Cruz. "Those are the views of New York."

In other campaigns, this sort of interview might be video dynamite. At one point in the full tape, Trump even points out that he'd have different views if he "lived in Iowa," mentioning the state as if to illustrate the idea's absurdity.

But as Trump came to dominate the primary, rivals attempted to make him own these comments — and failed. On Sept. 1, 2015, former Florida governor Jeb Bush released an 82-second compilation of old Trump statements, starting with the Russert interview. It has received nearly 1 million views, clocking them as Trump has continued to rise in polls and Bush has stalled in the high-single digits. In the newest polls from Iowa, Trump even leads Cruz among evangelical voters, despite the Texan's nearly unanimous support from evangelical leaders.

After trading jabs with his competitor for the Republican nomination for president on the campaign trail, candidate Jeb Bush posted an ad showing Donald Trump in a series of television interviews. (Jeb Bush)

But until now, no campaign had actually moved the abortion quotes from a free Web video into a paid TV ad. In a focus group convened by Frank Luntz last year, pro-Trump voters who saw the 1999 interview said that it was unfair to judge him for old statements after he'd evolved. And the antiabortion movement frequently absolves people who've changed their minds. The most famous convert might be Norma McCorvey, a.k.a. Jane Roe, the plaintiff in the 1973 case that legalized abortion in America. Since being baptized 21 years ago, McCorvey has campaigned to end legal abortion.

Trump, who in 1999 was considering a presidential bid with the briefly relevant Reform Party, has undergone a less dramatic evolution. As Buzzfeed's Andrew Kaczynski first noted, Trump actually backed down from the partial birth abortion answer within a year of the interview. "When Tim Russert asked me on Meet the Press if I would ban partial-birth abortion if I were president, my pro-choice instincts led me to say no," he wrote in his 2000 book, "The America We Deserve." "After the show, I consulted two doctors I respect and, upon learning more about this procedure, I have concluded that I would indeed support a ban."

In a statement accompanying the new ad, Keep the Promise pollster Kellyanne Conway ignored Trump's 2000 reversal, saying it should not "[take] 15 years to see it is a barbaric practice that takes the life of a child in the final weeks of pregnancy." In an interview, she said that Trump had not done enough to clarify that stance.

"Why doesn't he say that on the campaign trail?" she said. "I haven't seen him use his considerable media heft to give more visibility to the horror of partial birth abortion."

And this cycle, Trump has consistently opposed legal abortion, yet with more leeway and loopholes than anyone else in the primary. In August, when congressional Republicans were moving to cut all government funding for Planned Parenthood, Trump favored making the cuts "unless they stop with the abortions."

To many social conservatives, Planned Parenthood is an organization rooted in racism and eugenics, not worth funding under any circumstances. And Trump has missed other opportunities to find solidarity with antiabortion activists. On Friday, as a blizzard bore down on Washington, D.C., several Republican presidential candidates declared solidarity with the March for Life, the annual commemoration of Roe v. Wade. Trump never mentioned the march, though he did find time to retweet a user named "WhiteGenocideTM" who shared a photoshopped image of a decrepit-looking Jeb Bush outside of Trump Tower.

"The pro-life movement has been slapped and betrayed so many times before by people who claimed to be pro-life, but weren't active on the issue when they got to office," said Conway. "It's Donald Trump himself who has dredged up Bill Clinton's women, and all of those incidents pre-date this interview. Though I think Mr. Trump has boldly and correctly brought those incidents up, if they're fair game, so are statements of conscience he made in 1999."