Pres. Donald Trump took to Twitter on Sunday to lash out at Sens. John McCain (R-AZ) and Lindsay Graham (R-SC) after they spoke out against Trump’s bans of refugees and travelers from certain Muslim countries.

The two Republican senators issued a statement saying that Trump’s vaguely-worded, sweeping orders — which have thrown the country’s immigration system into “chaos” — were not properly vetted and are unconstitutional.

The Hill.com said Trump hit back on Twitter, writing, “The joint statement of former presidential candidates John McCain & Lindsey Graham is wrong – they are sadly weak on immigration.”

He went on, “The two Senators should focus their energies on ISIS, illegal immigration and border security instead of always looking to start World War III.”