As Donald Trump hurtles toward the Republican convention, he is on a collision course with the anti-abortion movement — a crucial conservative constituency that contends Republicans must own that issue to win a general election.

Leaders of the movement are suspicious, if not outright opposed, to the three-time married billionaire who only recently came to oppose abortion and whose gaffes suggest he does not understand the issue.

The latest flap exploded Thursday after Trump vowed he would “absolutely” change the Republican platform opposing abortion “for the three exceptions” — rape, incest and to protect the life of the mother. The platform is silent on exceptions, but anti-abortion groups such as March for Life shot back that Trump’s revisions would undermine the party’s “solidly pro-life” position.

“The suggestion that the platform should weaken its position on the pro-life issue would set back years of hard work in the pro-life movement,” said Tom McClusky, vice president of March for Life Action.

Add to that the GOP front-runner’s statements last month that women should be punished for getting illegal abortions and that he doesn’t want to change existing law — positions his campaign later recanted — which are anathema to a movement that portrays itself as supportive of pregnant women and seeks to overturn the Roe v. Wade decision legalizing abortion