North Dakota governor Doug Burgum has ended his campaign for the Republican US presidential nomination after a stronger than expected showing fuelled by a gift card-for-campaign donation gimmick that helped get him on the debate stage. Burgum, a second-term governor and wealthy software entrepreneur, was little known across the United States when he launched his 2024 presidential campaign in June, touting his priorities of energy, the economy and national security as well as his small-town roots and leadership of the sparsely populated state. He participated in the first two Republican debates, meeting donor requirements of the Republican National Committee by offering $US20 ($A30) "Biden Relief Cards" - a jab at rising inflation rates during US President Joe Biden's term - in exchange for $US1 donations. The tactic drew skepticism over its legality although Burgum's campaign said its legal advisers had reviewed and approved the method. He failed to qualify for the third debate, however, after coming up short on the polling requirements. And it appeared that he would also not qualify for the fourth debate, which is being held on Wednesday in Alabama. Indeed, he blamed the Republican National Committee, which sets qualifications for the debates, for "nationalising the primary process and taking the power of democracy away from the engaged, thoughtful citizens of Iowa and New Hampshire". "It is not their mission to reduce competition and restrict fresh ideas by 'narrowing the field' months before the Iowa caucuses or the first in the nation New Hampshire primary," he wrote in his statement announcing his departure. "These arbitrary criteria ensure advantages for candidates from major media markets on the coasts versus America's Heartland. None of their debate criteria relate to the qualifications related to actually doing the job of the president." Australian Associated Press