How is withdrawal from a toothless, unenforceable agreement more apt to "undermine the shared trust" (as if that ever existed) than ignoring the document altogether, which is what I though this administration might do.  It's a long way from "objectively sinful".  That particular theologian ought to have his / her teaching credentials revoked (unless that participant was not Catholic; a possibility, I suppose), an be held to public ridicule.
Make an enforceable treaty, submit it to the senate immediately prior to an election, advertise the heck out of it to get voters to pressure congress on the issue, let the chips fall where they may.