Lindsey Graham, a longtime US senator and key ally of Donald Trump, has died from a sudden illness, his office said in the early hours of Sunday. He had just turned 71.

Graham’s abrupt death will send shockwaves through Washington and the Republican party. He had served in the Senate since 2003, representing South Carolina, and was running for re-election in November.

“On the evening of Saturday, July 11, US senator Lindsey Graham passed away from a brief and sudden illness,” his office said in a statement. “Senator Graham’s family appreciates prayers at this time and asks for privacy during this incredibly difficult period.”

There had been no known concerns over the health of Graham, who last week visited Ukraine. On Friday its president, Volodymyr Zelenskyy, wrote on social media that they had a “good meeting”, adding: “I’m grateful to Lindsey for recognizing our warriors.”

Graham, a retired air force reserve colonel who specialised as a military lawyer, was known as a hawk who supported the Iraq war and had long urged military action in Iran. He opposed the nuclear agreement negotiated by President Barack Obama and has been one of Trump’s most outspoken defenders in the current conflict.

He ran for president in 2016 and was a sharp critic of Trump at the time. Graham condemned Trump as a “jackass”, “a race-baiting bigot” and “the most flawed nominee in the history of the Republican party”, memorably warning on Twitter:“If we nominate Trump, we will get destroyed … and we will deserve it.” Trump, in turn, dismissed Graham an “idiot” and a “lightweight”.

But once Trump became unassailable, Graham became a valued ally who could act as an interlocutor between the president and Congress. In 2018 he rallied the defence of Trump’s embattled nominee for the supreme court, Brett Kavanaugh.

Graham wobbled only after Trump’s supporters staged an insurrection at the US Capitol on 6 January 2021 in an effort to overturn his election defeat. The senator declared: “Trump and I, we’ve had a hell of a journey – I hate it to end this way. Oh my God, I hate it. From my point of view, he’s been a consequential president but today, first thing you’ll see. All I can say is count me out. Enough is enough.”

His rebellion did not last, however, and he refused to vote to convict Trump at the subsequent impeachment trial. He was again quick to endorse Trump in the 2024 presidential election and often played golf with him.

Graham’s death marks the passing of the last of the “three amigos”, comprising Graham, Joe Lieberman and John McCain, senators and close friends who each made unsuccessful bids for the presidency. McCain died in 2018, Lieberman in 2024.

Among those paying tribute on Sunday was Henry McMaster, the governor of South Carolina, who said in a statement: “Lindsey Graham is irreplaceable. The fiercest of fighters for South Carolina and America – and a loyal and steadfast friend.”

Several leaders in Israel expressed condolences. Itamar Ben-Gvir, the national security minister, posted on X: “Today, Israel has lost one of its greatest friends. Senator Lindsey Graham stood with Israel not because it was easy, but because he believed it was right. His unwavering support, courage, and moral clarity earned him the admiration of millions of Israelis.”

Naftali Bennett, a former prime minister, added: “America has lost a devoted patriot, and Israel has lost one of its greatest friends. Lindsey stood with Israel through our darkest hours, with courage.”