GOP Senate candidate Ben SasseBenjamin (Ben) Eric SasseFrequent Trump critic touts president: Trump's rhetoric on free trade at G-7 is 'tremendous news' Overnight Defense: Trump draws ire for wanting Russia back in G-7 | Movement on defense bills expected next week | Air Force grounds B-1 fleet over safety issue Top EU figure: Trump is ‘undermining’ world order the US created MORE announced Thursday he raised more than $850,000 in the first quarter of the year, significantly more than his main challenger in the race.

Sasse made the announcement on Twitter.

His campaign went on to announce in a press release that he has over $1 million cash on hand.

Another Republican candidate, Shane Osborn, revised his previously-announced fundraising numbers upwards to $610,000 raised in the quarter, with $715,000 cash on hand.

Osborn is a former state Treasurer and Navy pilot and is one of two frontrunners in the race, along with Sasse, who serves as president of Midland University.

Last week, conservative group FreedomWorks withdrew its endorsement of Osborn and said it would support Sasse instead.

They are among four GOP contenders vying for the seat Sen. Mike Johanns (R-Neb.) will leave when he retires at the end of the year. It’s expected to remain in Republican hands.

—This piece was updated at 9:30 to reflect Osborn's revised numbers.