Cramer told The Associated Press he would make a decision by the weekend, adding "I don't want to let this linger."
"People are apparently concerned Republicans can't win," Cramer said. "I've always believed I have the best chance to win but I'm not the only chance to win."
Cramer is a staunch advocate of President Donald Trump and has been considered a formidable opponent for Heitkamp, whose perceived political independence and personal charm has made her personally popular with North Dakotans.
Republicans hold a 51-49 Senate majority. 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 narrowly won her first term in 2012 in a heavily conservative state.
State Sen. Kelly Armstrong, who heads the North Dakota GOP, said Cramer is the party's "best hope" of defeating Heitkamp in November.
"Kevin has built in advantages," Armstrong said. "He is popular statewide and he has a proven record at the federal level."
Despite a personal appeal from Trump, Cramer announced in January he wouldn't run for Senate, citing family considerations and his House seniority. Cramer said that he has since been contacted by GOP faithful and "hundreds" of North Dakotans to get into the race, fearing if he doesn't it could hurt the already thin majority in the Senate.
"That has put added weight that I didn't think about before," he said. "I'm now looking at it through a patriotic lens."
Cramer said billionaire oilman Harold Hamm has been encouraging him to run against Heitkamp and has "committed" to being his finance chairman if he runs.
"That was part of his encouragement," Cramer said of the oil tycoon, who already served as his finance chairman during his successful bid for U.S. House in 2012. "Harold and North Dakota obviously are hand-in-glove and he is the godfather of the Bakken oil."
Hamm is the chairman of Oklahoma City-based Continental Resources Inc., which is one the oldest and biggest oil drillers in North Dakota. Hamm also endorsed Donald Trump for president and had been under consideration for energy secretary.
Cramer said if he does run for Senate it would be an "opportunity for North Dakota to contribute to the national Trump agenda." Trump carried the state by 36 points in 2016 and remains popular.
Cramer, 56, is a former state Republican director and chairman. He ran twice for the House in the 1990s, losing to incumbent Democrat Earl Pomeroy in 1996 and 1998 before winning it in 2012.
Cramer has been teasing reconsideration for Senate since late last week. On Tuesday, Republican Gary Emineth quit the race, saying he'd spoken with Cramer several times recently and expected him to challenge Heitkamp.
"He's getting a lot of pressure from Washington," said Emineth, a close friend of Cramer's who ran his congressional campaign in 2012.
Emineth's departure left Tom Campbell, a second-term state senator who trails Heitkamp badly in name recognition and money, as the only Republican in the race.
Armstrong, the state Republican chairman, said the GOP would still have a shot at defeating Heitkamp if Cramer does not run because she is a Democrat in a heavily Republican state.
"We are a red state with a blue senator - people are going to get involved," he said.
Campbell has 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.
Cramer said he would have no problem raising money for a Senate bid.
"This is a high-profile race - I would have more than enough money to win," he said.
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