WASHINGTON — The last time President Trump vowed all-out retaliation against Mexico for the illegal immigrants crossing the border, he backed off. In April, he gave America’s southern neighbor a year to fix the problem.

It turns out he cannot wait that long.

As he ratchets the pressure back up with threats of a tariff war, Mr. Trump once again finds himself grasping for ideas to deliver on his signature campaign promise: ending illegal immigration, no matter how incendiary or legally dubious. With an election year approaching, he appears increasingly anxious to get a handle on the problem and show results.

Time and again, the president has engaged in a game of geopolitical chicken with Mexico, warning darkly of radical measures that even his own advisers caution him against. His latest scheme would impose escalating tariffs on all imports from Mexico, a move that could blow up the economic relationship with one of America’s closest neighbors. But there was no more guarantee that will be any more effective than his past efforts, or that he will even necessarily follow through with his threat.

“This is yet another flailing about in an effort to effect a change he’s failed to bring about,” said Roberta S. Jacobson, a former career diplomat who served as ambassador to Mexico for the first year of Mr. Trump’s presidency. “Every time he sees something like ‘highest total in one week in X years,’ he demands something, and his advisers come up with something even more extreme, and he goes for it.”