Does he, or did he — and does the distinction matter? An anti-Trump PAC takes aim at the source of Donald Trump’s strength in the primary battle by arguing that Trump has backed “amnesty” — and enriches himself through illegal-immigrant labor. Reid Epstein reports in the Wall Street Journal that $1 million will go into Iowa television markets behind this 60-second spot:

https://www.youtube.com/watch?v=Enw6Yx19qSg

The latest TV ad broadside against Republican presidential front-runner Donald Trumpfeatures footage of him backing citizenship for undocumented immigrants after his campaign launched and accused him of profiting from illegal workers.

The new 60-second ad is part of a $1 million Iowa TV ad buy from Our Principles PAC, an anti-Trump group run by former Mitt Romney aide Katie Packer. …

But the ad contains footage from a late June Chicago appearance in which Mr. Trump appears to favor allowing illegal immigrants a pathway to citizenship.

“You have to give them a path and you have to make it possible for them to succeed,” Mr. Trump says in the ad. “You have to do that.”

To make its point, the ad pulls from sources that range from 1990 to July 2015. The older sources go to the use of immigrant labor in building Trump’s hotels, although there is more on that from last year, too. The sources on Trump’s positions on “amnesty” come from 2013 and June of last year, both close enough to present day to potentially raise questions about Trump’s credibility on the one topic that has raised him to front-runner status.

The tweet in 2013 came at the same time that Marco Rubio put together the Gang of 8 deal on immigration in the Senate, for which voters and other Republican candidates have punished him ever since. Trump’s 2013 tweet basically summarizes the Gang of 8 approach — secure the borders, then legalize most of the remaining illegal immigrants after background checks and fines, which some consider “amnesty.” The June 2015 statement appears to go a little farther in providing a “path,” presumably to citizenship, and Trump made that statement in the context of the presidential campaign. The difference might be that Trump wants a “touchback” first — deportation followed by immediate readmission — but that would be almost impossible to accomplish, and in the end no different in substance than the Gang of 8 deal which GOP voters mainly opposed.

Of course, Trump has changed positions on lots of issues without losing the support of his voters. This could be different, but it’s almost certainly more aimed at Trump-leaners than committed Trump voters, following the strategy of attacking opponents on their strengths more than their weaknesses. Trump’s strength isn’t immigration as much as it is authenticity. If Trump’s opponents can erode that authenticity, especially on his strongest policy position, they might peel away enough enthusiasm to leave Trump vulnerable in Monday’s caucuses. Maybe. But don’t expect those voters to jump to Rubio if and when they peel off from Trump. Cruz would be the most likely beneficiary of any damage this ad does.