(CNN) Senate Republicans remained sharply split Thursday on how to structure a debate over a disapproval resolution on President Donald Trump's declaration of a national emergency, just days before they must vote on the measure, which is expected to pass.

"We are having a robust discussion," said Sen. John Cornyn, a Texas Republican, as he emerged from a closed-door meeting in the Capitol. "Lots of ideas, great ideas. But no conclusions."

At issue is whether and how to amend the disapproval language that passed the Democratic-controlled House -- or consider companion legislation -- to make it more palatable to GOP senators before they vote.

Republicans support or oppose Trump's declaration for a variety of constitutional, policy and political reasons. Some think the emergency declaration, through which Trump is repurposing existing funds to build a border wall with Mexico despite Congress voting down his request, is an unconstitutional power grab. Others worry it sets a dangerous precedent that future presidents could use anytime they lost a negotiation with Congress.

Before Thursday, Republicans weren't even sure if parliamentary rules would allow them to amend the disapproval measure, which is being used for the first time.

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