Republican presidential front-runner Donald TrumpDonald TrumpIran's leader vows 'revenge,' posting an image resembling Trump Former Sanders spokesperson: Biden 'backing away' from 'populist offerings' Justice Dept. to probe sudden departure of US attorney in Atlanta after Trump criticism MORE on Monday was spotted grabbing lunch with Edward Klein, the author of several books critical of Bill and Hillary ClintonHillary Diane Rodham ClintonSamantha Power's Herculean task: Turning a screw with a rubber screwdriver Beau Biden Foundation to deny lobbyist donations, make major donors public Whoopi Goldberg wears 'my vice president' shirt day after inauguration MORE.

Trump, joined by aides Corey Lewandowski and Daniel Scavino, sat for a quick lunch at a delicatessen in Indianapolis, according to The Washington Post.

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The Post reported Klein was riding in the same vehicle as Trump. Klein said he was following Trump for a couple of days, gathering material for a new book.

Klein’s work on the Clintons has repeatedly come under attack for playing loose with the facts even as it has risen to the top of the best-sellers lists.

Klein wrote a book in 2014 claiming that Hillary Clinton was suffering from a heart problem after previously writing on her husband and former President Bill ClintonWilliam (Bill) Jefferson ClintonMcConnell proposes postponing impeachment trial until February The Hill's Morning Report - Biden takes office, calls for end to 'uncivil war' The Memo: Biden strives for common ground after Trump turmoil MORE's sexual history. 

The meeting comes amid Trump's push to move past rivals Ted CruzRafael (Ted) Edward CruzFor Biden, a Senate trial could aid bipartisanship around COVID relief Senate Democrats file ethics complaint against Hawley, Cruz over Capitol attack Poll: Majority of voters support bipartisan commission to probe potential irregularities in the 2020 election MORE and John Kasich to clinch the GOP nomination and put his focus on attacks aimed at Hillary Clinton, the likely Democratic presidential nominee.

Trump is campaigning in Indiana ahead of the state's  Tuesday primary.