Republicans in the Senate are desperate to avoid another debilitating government shutdown but dread crossing President Trump on immigration, fearing a break with the White House could boomerang against them with the conservative base in 2020.

This dilemma raises the stakes for Senate Republicans as bipartisan border security negotiations begin in a bicameral congressional committee. They have to squeeze the best possible deal from confident Democrats, who oppose Trump’s top priority — building a wall along the Mexican border — and are convinced shutdown politics play to their advantage. Then, Republicans have to hope the notoriously fickle Trump approves and abandons threats to partially shutter the government again.