In New Hampshire, a retired general who openly supports Donald Trump won the party's nomination for the Senate.
In November, Democrat Maggie Hassan will square off against Don Bolduc; according to pundits, Hassan may lose her seat.
Republicans may be able to retake the majority in the Senate if they defeat the incumbent and earn the additional seat.
Trump-supporting candidates also prevailed in the two primaries held in each state for the House of Representatives, which is the lower house of Congress.
Mr. Bolduc, a veteran of ten tours in Afghanistan, has made unfounded claims that Donald Trump won the 2020 presidential election and that coronavirus vaccines contain microchips.
In the same period of time that Ms Hassan has accumulated more than $31 million, the 61-year-old has also raised less than $600,000 (£514,000) from small-scale donors.