Senator Lindsey Graham said on Monday if President Donald Trump declares an emergency to fund a wall on the US-Mexico border it could provoke a war in the Republican party, and urged fellow Republicans to back the "commander-in-chief."Speaking to reporters in Greenville, South Carolina, Graham said he was not convinced Congress could reach a deal to give Trump the $5.7 billion he is seeking to fund a border wall."I'm not very optimistic we're going to get a deal. It seems to me that he's going to have to go it alone" by declaring an emergency, Graham said. "But there could be a war within the Republican Party over the wall."Senate Majority Leader Mitch McConnell is reported to have told Trump that it was possible that some Republicans in the Senate would join minority Democrats to pass a resolution to block any emergency declaration, which Trump would then have to veto."Any Republican who denies the president the ability to act as commander-in-chief, you're going to create a real problem within the party," Graham said.