President Biden has come to recognize that the surge of undocumented immigration during his presidency is a threat to his re-election. He knows that most voters are unhappy about the increase. So are mayors and governors who have been left to deal with an expensive and often chaotic situation — such as in Denver, the subject of a recent Times story.

Biden and his advisers have already settled on one strategy to reduce his political vulnerability. They plan to remind voters that congressional Republicans this month blocked a bipartisan bill that would have strengthened border security. Even though many Republicans favored the bill’s policies, they defeated it at Donald Trump’s behest, largely to avoid solving a problem that has hurt Biden politically.

Given the blatantly partisan nature of the Republicans’ decision, it’s reasonable for Biden to emphasize it during his campaign. But I would be surprised if he could eliminate his vulnerability on immigration merely by criticizing Republican intransigence.

Why? Biden is the president, after all, and a president has significant authority to shape immigration policy even without new legislation.

Biden himself has been aggressive about using this authority — albeit to loosen immigration policy rather than tighten it. During his first months in office, he expanded asylum and paused deportations. He also expanded a policy known as parole, which the law says should be used “only on a case-by-case basis.” Last year, Biden used parole to admit more than 300,000 people.

These policies, combined with Biden’s welcoming rhetoric during the 2020 campaign, contributed to the migration surge. (John Judis went into more detail in a recent Times Opinion essay, as did David Ignatius in a Washington Post column.) The changes signaled to migrants that their chances of being able to enter and remain in the U.S. had risen.