Another one bites the dust. The past few weeks had been billed as a retribution tour for Donald Trump, as he settles old scores with his critics within the Republican party. Call it what you will, but the evidence is now overwhelming that the Republican party is Trump's party and nothing - not an unpopular war in Iran, not sagging poll numbers among the general public, not rising consumer prices, not concerns about billion-dollar White House ballrooms - has changed that.

Thomas Massie, the independent-minded congressman from Kentucky, was comfortably defeated on Tuesday in the Republican primary race to decide who goes forward to take on the Democrats in November's midterms. The Trump-backed candidate Ed Gallrein is heading towards a 55% share of the vote.

Republican rebel Massie, a constant thorn in Trump's side, is just the latest in a political casualty count that is now stretching into double figures. His transgressions were multitude. He opposed Trump's tax-and-spending budget package last year because he said it drove up the federal deficit. He voted to curtail the president's military operations in Venezuela and Iran. And, perhaps most notably, he was the driving force behind efforts in the House of Representatives to force the release of Justice Department files on Jeffrey Epstein, the disgraced financier and sex offender with ties to the rich and powerful.

All this put Massie front and centre on Trump's enemies list – and led to a $20m effort to oust him from the congressional perch he had occupied for more than a decade.

Trump once again proved his power in the Republican party, with Massie's defeat underscoring his influence. Gallrein, Massie's handpicked Trump opponent, barely campaigned. He declined most debate and public forum invitations. He instead relied on the president's endorsement and millions of dollars of support it generated. That proved to be enough – and it wasn't all that close, as the challenger coasted to what appears to be a double-digit victory.

Massie now joins Louisiana Senator Bill Cassidy, who lost to a Trump-endorsed rival in a Republican primary on Saturday, and five of seven Indiana state legislators opposed by the president last week among the ranks of the soon-to-be-unemployed politicians. Next Tuesday, another incumbent senator, John Cornyn of Texas, may join them as Trump endorsed his opponent in the upcoming runoff election.

Unlike Massie, who openly challenged Trump, and Cassidy, who voted to convict Trump during his impeachment trial, Cornyn had not clearly broken with the former president. However, Trump's late endorsement of Paxton surprised many Republicans and showcased his willingness to target incumbents.

Although Trump is steadily removing his critics from within the Republican Party, the defeats also highlight a potential risk as many of these loyal Republicans may not perform well in the general elections, where broader voter support is critical.