"Darren is just the man to take on and defeat one of the worst governors in America, JB Pritzker. He's one of the worst," Trump said.
A large majority of Illinois Republicans said they admire Trump, and Bailey said his backing is giving him a big boost.
"Propelling us into national headlines, people are aware. So, now they're following up. Even our own Twitter and Facebook messages that I am receiving," Bailey said. "I think it's going to be good for turnout, and that's what we've got to have."
Bailey, a strong pro-lifer, is still saluting the Supreme Court's Dobbs ruling sending the issue of abortion back to state governments to decide.
Former Republican Gov. Jim Edgar, who is pro-choice on abortion, noted that a majority of Illinois voters are too. He fears Bailey won't be able to win over many of those voters in the general election.
"People can complain maybe they don't like what some of us did back in the eighties and nineties. But we won, and we governed," Edgar said "If the party continues its move to the right, we will be a permanent minority party in Illinois."
A half-dozen voter opinion surveys have shown Bailey building a big lead over the last three weeks, with tech investor Jesse Sullivan moving into second place ahead of former front-runner Richard Irvin, the mayor of Aurora.