HELENA — U.S. Sen. Jon Tester added another $2 million to his campaign war chest as he prepares to face his eventual Republican opponent.

The two-term senator from Big Sandy is expected to have one of the fiercest re-election battles in 2018, and he has been feverishly raising money.

Ahead of Friday’s latest fundraising reporting deadline, his campaign said he already had $4.7 million in hand as of June 30.

His $2 million take since April 1 adds to a similar amount he reported to the Federal Election Commission for the first quarter of the year.

A Republican front runner has yet to emerge, as top-tier candidates have decided against running, including state Attorney General Tim Fox and former U.S. Rep. Ryan Zinke. Zinke was an obvious first choice for the GOP until he became President Donald Trump’s Interior Secretary.

Montana Democrats are now taking aim at Auditor Matt Rosendale, who has been coy about his intentions. He’s said that he will make a decision over the summer.

“Regardless of who makes it through the primary, there’s no question it’s going to be a very tough race,” said Chris Meagher, a state Democratic Party spokesman who has been fielding press calls for Tester’s campaign. “I also know whoever runs against Jon is going to have a tough race themselves.”

With less than a year before the Republican primary, potential GOP contenders will have to make a decision soon to begin building the campaign infrastructure and financial backing to mount a serious campaign.

Democrats have also shown concern about a possible run by District Judge Russell Fagg of Billings, a former state legislator, who has formed an exploratory committee. Fagg earlier announced that he would be stepping down from the bench in October and has said he would not make a formal announcement about a Senate bid until then.

A handful of lesser-known Republicans have also expressed interested in Tester’s seat, which handicappers say could be among the most competitive next year.