The former House speaker and 2012 Republican presidential candidate made a surprise appearance at an event for Ohio Gov. John Kasich in Arlington, Virginia, on Tuesday -- the day GOP voters in 11 states will vote in the presidential nominating contest.
Gingrich's appearance was not an endorsement, Kasich campaign spokesman Chris Schrimpf confirmed.
Earlier in the day, House Speaker Paul Ryan had repudiated Trump, saying that "this party does not prey on people's prejudices" and that "if a person wants to be the nominee of the Republican Party, there can be no evasion and no games."
Gingrich, though, said he didn't think Trump had meant to be evasive when he didn't disavow the support of former Ku Klux Klan grand wizard David Duke when asked three times about it by CNN's Jake Tapper on "State of the Union."
The former speaker noted that Trump had disavowed Duke in the past -- including two days before the interview -- and did again after the CNN interview.
"Trump repudiated him on Friday, he repudiated it in 2000, he repudiated him Monday morning on the 'Today' show and he clearly messed up on CNN Sunday," Gingrich told CNN in an interview at the Kasich event. "We'll find out by the debate Thursday night, Trump's going to handle the questions ... I think Trump probably agrees with Ryan that you have to condemn racism."
Still, Gingrich said, he's not surprised other candidates are taking swipes at Trump over his handling of the questions about white supremacists' support.
"The other candidates are trying to take advantage a mistake and that's what they should do," he said.
Gingrich had tough words for the GOP establishment, pointing out that, combined, Trump, Texas Sen. Ted Cruz and Ben Carson have about 70% support from voters, according to polls.
"Now at some point, the establishment has to say, 'Gee, if we've lost 70% of our base, maybe we need to rethink what we're doing,' " he told CNN.
Of the Trump phenomenon, Gingrich said: "I think it's historic and extraordinary and something people should study."