Gary Emineth said he's talked with Cramer several times in the past week and expects him to enter the race.
"He's getting a lot of pressure from Washington," said Emineth, who is a close friend of Cramer's and ran his congressional campaign in 2012.
Despite a personal appeal from President Donald Trump, Cramer announced in January he wouldn't run for Senate, citing family considerations and his House seniority.
Cramer did not respond to messages from The Associated Press on Tuesday. He told radio station KFGO on Tuesday night that he is reconsidering a run for the Senate and plans to make an announcement by the end of the week.
Emineth announced his bid after Cramer said he was skipping the race. Emineth's departure comes less than a week after he defended himself for deleting more than 100 of his social media posts soon after he got in the race, including one that called anti-Israel protesters "a bunch of Arabs."
Emineth's departure leaves state Sen. Tom Campbell as the only major GOP opponent to Heitkamp, and he has challenges of name recognition and money.
Campbell, a state senator and potato farmer, dug deep into his own pocket in recent months to buy TV ads to raise his profile statewide. Almost three-quarters of the more than $1 million he has raised has come from himself, Federal Election Commission filings show.
Heitkamp has raised about $7.7 million and has about $4.4 million cash on hand.
Heitkamp is among 10 Democrats in states Trump carried who are up for re-election in 2018. The former state attorney general and gas company executive opposed Trump on some issues but sided with him on others, especially on coal and oil questions important to North Dakota.
Cramer is a staunch Trump advocate and has been considered the only Republican capable toppling Heitkamp, whose perceived political independence and personal charm has made her personally popular with North Dakotans.
State Sen. Kelly Armstrong, who heads North Dakota's GOP party, said Cramer's campaign manager, Jared Hendrix, told party faithful at a district convention Monday night that the congressman was "reconsidering strongly" running for the Senate seat.
"That was the elephant in the room in a room full of Republicans," Armstrong said.
Hendrix did not immediately respond to messages from the AP on Tuesday.
"I think Kevin is really, really torn over this but I think there is call from the White House for a call to service for his country and the state," Armstrong said.
Cramer, 56, is a former state Republican director and party chairman. He ran twice for the U.S. House in the 1990s, losing to incumbent Democrat Earl Pomeroy in 1996 and 1998, before winning it in 2012.
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