U.S. Rep. Doug Collins will soon announce a challenge to U.S. Sen. Kelly Loeffler, setting up a bitter Republican showdown in November that pits one of President Donald Trump’s most vocal defenders against a wealthy former executive backed by Gov. Brian Kemp.

Collins, who is set to be at the Georgia Statehouse on Tuesday, has started to line up campaign staff and call politicians and supporters to inform them of his decision to enter the race, according to several people who received the calls but requested anonymity to discuss private conversations.

The four-term congressman hopes to launch his campaign with support from Trump’s inner circle, if not the president himself. Trump privately lobbied Kemp on at least three separate occasions to tap Collins to fill the coveted seat, though he’s stayed publicly neutral since Loeffler was sworn into office.