A politically treacherous dynamic is taking hold as negotiators in Congress work to strike a bipartisan deal on the border and immigration, with vocal opposition from the hard right and former President Donald Trump threatening to topple the carefully negotiated compromise.

Senators are closing in on the details of an agreement on border measures that could unlock Republican support for Ukraine aid and hope to unveil it as soon as next week. But the deal is already wobbling, as House Speaker Mike Johnson faces intense pressure from Trump and his House allies to demand more sweeping concessions from Democrats and the White House.

“I do not think we should do a Border Deal, at all, unless we get EVERYTHING needed to shut down the INVASION of Millions & Millions of people,” Trump posted on social media this week.

It’s a familiar political dynamic, one that has repeatedly thwarted attempts to reform U.S. immigration law, including in 2013 when House Republicans sought to pin illegal immigration on a Democratic president and in 2018 when Trump helped sink another bipartisan effort. The path for legislation this time around is further clouded by an election year in which Trump has once again made railing against illegal immigration a central focus of his campaign.