The Senate is poised to challenge President Trump this week with legislation requiring the military to rename bases bearing the names of Confederate generals, a proposal that is shaping up to be one of the most contentious items in this year’s annual defense bill.

In the Senate, the main issue appears to be timing. The bill that emerged from the Republican-led Senate Armed Services Committee included a provision giving the Pentagon three years to come up with new names, while an amendment filed by Sen. Elizabeth Warren (D-Mass.) and 35 other Senate Democrats last week would speed up that process, requiring the name changes within a year.

Although there is still vocal opposition to removing the Confederate names — Sen. Josh Hawley (R-Mo.) has proposed an amendment to strip the renaming requirement — Republican support for the measure suggests that it will survive any challenges during this week’s floor debate.

But with Trump pledging that he will “not even consider the renaming” of bases, it is possible that the provision could eventually pitch Congress into a showdown with the president over the entire defense bill.

The push to rename the 10 major bases named after Confederate generals — and remove other Confederate likenesses, symbols and paraphernalia from all defense facilities — has gained momentum as nationwide demonstrations against racial injustice and police brutality enter their second month.

Protesters have pulled down several public statues of Confederate figures and slave owners, drawing a mix of praise from those who think that their removal is overdue and criticism from others — including Trump — who argue that it is an affront to history and “law and order.”

The annual defense bill is one of the few “must pass” measures Congress considers every year, and if this year’s proposed $740 billion behemoth passes, it will be the 60th consecutive year that lawmakers have approved the measure. But because of its special status, the legislation frequently becomes a focal point for political debates. In election years especially, that can mean long, drawn-out battles in each chamber, and between the Senate and the House as they work out the differences between their versions.

In the Senate, Armed Services Committee Chairman James M. Inhofe (R-Okla.) has indicated that he wants a final vote on that chamber’s bill before lawmakers leave Capitol Hill for the two weeks following July 4.

But in the House, the defense bill process still has a long way to go. The Democratic-led House Armed Services Committee just published its proposed measure last week, and it was curiously silent on the matter of renaming bases bearing Confederate generals’ names. But the matter is likely to come up when the panel reviews the bill Wednesday, along with any amendments to it.

Last year, the House included a measure in its version of the defense bill prohibiting Pentagon leaders from naming any Defense Department assets after any member of the Confederacy or site of a Confederate battle victory.