When a jubilant JD Vance claimed victory as the newly elected US Senator for Ohio, he told a relieved state Republican party that he was “overwhelmed with gratitude”.

The bestselling author of Hillbilly Elegy, an account of growing up amid drug addiction and poverty, thanked his family, his campaign team and his fellow Republican candidates in the midwestern state. But all of that gratitude did not extend to a mention of the one person Vance arguably owes most to, Donald Trump.

It was the former president’s endorsement that dragged Vance from the back of the Republican primary field earlier this year and delivered him the nomination. But after that, Trump’s attempt to maintain his grip on the Republican party by playing kingmaker was of dubious value, as many of his other favoured candidates found out when the midterm election results rolled in.

At least Vance won, although the evidence is that Trump hindered him among the broader electorate as the venture capitalist took a smaller share of the vote than most other Republicans running for statewide office in Ohio.

Other more outlandish candidates backed by Trump went down in flames in what might otherwise have been regarded as winnable seats on a night when the Republicans, far from riding the much promised “red wave”, were instead left becalmed and wondering if they could hang on to what they already have.

In Pennsylvania, one of the most closely watched Senate races pitched the Trump-backed celebrity Mehmet Oz, known on television as Dr Oz, against John Fetterman, a Democrat who had to overcome voter scepticism about his ability to serve after suffering a stroke.

Fetterman snatched the crucial seat from the Republicans as exit polls showed some voters thought Oz was the one who was unfit for the office. They also said that he was damaged by being from New Jersey.

In Arizona’s race for the Senate, a state Trump narrowly lost in 2020, the former president backed Blake Masters, a venture capitalist and a protege of the rightwing billionaire businessman Peter Thiel. Masters won favour with Trump by claiming that the 2020 election was stolen and that he would have refused to certify the result if he had been a senator.

With two-thirds of the vote counted, Masters was trailing the Democratic incumbent, former astronaut Mark Kelly.

In other races, Trump’s endorsement did not produce the decisive win the Republican candidates hoped for. In Wisconsin, Senator Ron Johnson eked out a slim victory in a state where elections are often narrowly decided, suggesting Trump was of no great help.

Similarly, Trump’s candidate in Georgia, Herschel Walker, was headed to a runoff next month against the sitting Democratic senator, Raphael Warnock, when Republicans had hoped for a clear victory with the former president’s support.

In Nevada, the fiery pro-Trump Republican contender, Adam Laxalt, was in a tight race with the sitting Democratic senator, Catherine Cortez Masto.

Contests for the House of Representatives produced some disappointment for the Trump camp too. In Colorado, Congresswoman Lauren Boebert, described as the “Trumpiest of Trumpists”, was struggling to hold on to her seat as the final votes were tallied on Wednesday.

For all that, the new Congress will still be have dozens of members who continue to deny Trump lost the 2020 presidential election among more than 200 Republicans elected to offices across the country who continue to question Biden’s victory as most were re-elected. Among them was an Arizona congressman, Andy Biggs, who has denied that he asked Trump for a pardon over his part in the storming of the Capitol on 6 January 2021.

Hans Hassell, an associate professor of political science at Florida State University, who has investigated the impact of Trump’s endorsements on elections, said that the limitations of the former president’s support should come as no surprise. His research on Trump’s endorsement in the 2018 midterms showed that it was just as likely to mobilise opposition as support.

“In those particular races, we found that when Trump endorsed a candidate, it was a boost in terms of their fundraising ability but it also mobilised the opposition dramatically. The opponents of Trump’s endorsees actually received more money than than the Trump-endorsed candidate did. Ultimately, those candidates that Trump endorsed, they did worse than non-Trump-endorsed candidates,” he said.

“Trump’s endorsements are not random. They are strategic. He tries to endorse candidates that will boost his perceptions of influence. But on the whole a Trump endorsement was a negative in 2018 in terms of the vote shares and probably lost Republicans 15 to 20 seats as a result of that races where he endorsed.”

This year, part of the Trump camp’s strategy for his expected 2024 presidential run was to place supporters in key positions, particularly in swing states, that have influence over the conduct of the vote, and the count. But that also fell short as Trump’s endorsement appears to have damaged Republican chances in several races for state governor by pushing weak candidates to the fore.

In Pennsylvania, Doug Mastriano, a retired army colonel who enthusiastically promoted Trump’s false election rigging claims, was soundly beaten as were other election denying candidates for governor in Wisconsin, Maryland and Massachusetts.

In Arizona, Kari Lake, a Trump favourite who said she would be the media’s “worst fricking nightmare” if elected, was narrowly trailing her Democratic opponent to replace the retiring Republican governor.

Similarly, Trump’s people lost in contests for secretary of state in several places where that would have given them oversight of the 2024 presidential vote.

Mark Finchem, a member of the Oath Keepers militia, was behind in Arizona as was Trump’s candidate for the state’s attorney general position, which also has influence over elections.

In Michigan, Kristina Karamo, who claimed to have witnessed ballot tampering during the count in Detroit in 2020 and was part of an unsuccessful lawsuit to overturn the election, lost her bid to become secretary of state.