Arizona was the rusted on red state that hardly ever turned blue. In the past seven decades it has gone Democrat in a presidential election on just one other occasion.
Mr Trump should have held it – like he did North Carolina and Florida – but he blew it. And some have said he failed in Arizona because of a litany of unnecessary insults against one of the state’s favourite sons.
An attack on late Republican former presidential candidate John McCain is seen by some in Arizona as an attack on the whole state.
Arizona’s loss “could be the revenge of John McCain,” said the senator’s former adviser Mike Murphy on new channel MSNBC, when it was still up in the air whether the state would fall.
Mr McCain’s widow Cindy released a statement after the declaration saying she was “proud of the voters of Arizona,” and Mr Biden was a “man of honour” who she had been friends with for 40 years.
She didn’t mention Mr Trump by name at all. Rather she said she hoped the president-elect could “heal the wounds caused by the outgoing administration”.
Congrats to @JoeBiden for carrying my home state of Arizona. I am so proud of Arizonans for showing up in record numbers to make their voices heard. Thank you to the election workers who ensured a fair and honest process. Let’s get to work!https://t.co/ePhuwhVX40
Mr McCain, who ran for president against Barack Obama in 2008, was a war hero who was imprisoned and tortured in Vietnam.
And he was a thorn in President Trump’s side.
He refused to endorse Mr Trump during his 2016 presidential run and his 2017 vote on the Senate floor torpedoed plans by the administration to do away with large swathes of President Obama’s healthcare reforms.
Mr Trump was apoplectic with rage. “What he did to the Republican Party and to the nation and to sick people that could have had great healthcare was not good …. I’m not a fan of John McCain, and that’s fine.”
But Mr Trump had long made his feelings about Mr McCain known – shocking members of his own party as well as voters in the senator’s home state.
In 2015, when his presidential run was still gathering pace, the TV host laid into Mr McCain’s war record.
“He’s not a war hero,” he said to supporters in Iowa.
“He was a war hero because he was captured.
“I like people who weren’t captured.” Just six words that dismissed Mr McCain’s heroism and all his suffering as a prisoner of war. Arizona did not forget.
Of course, Mr Trump was never captured during service. Because he never served.
Mr McCain was also a centrist Republican. He was in favour of LGBT rights and some gun controls and preferred consensus and pragmatism over blind loyalty to a party or President.
Mr McCain died of brain cancer in 2018, aged 81. Former presidents Obama, Bush, Clinton and Carter all attended. President Trump was not invited.
He issued a single, terse tweet that sent his "deepest sympathies and respect" to the family without any words for McCain himself.
At another memorial for the senator in Phoenix, Arizona’s largest city, then Vice-President Biden took to the lectern.
“My name is Joe Biden. I’m a Democrat. And I loved John McCain,” he told his audience. Arizona remembered.
Months after Mr McCain’s death, Mr Trump lashed out at the late senator again - four times in five days including claiming he, “didn’t get a thank you,” for allowing a state funeral.
But the cathedral which held the service said the funeral was not Mr Trump’s to approve as Mr McCain had never been President.
Republican Senator Johnny Isakson rebuked Mr Trump at the time.
“It’s deplorable what he said. We don’t talk about our veterans in any way but to brag on them for the service they render,” he said in a radio interview.
Arizona’s loss to the red column cannot be put down entirely to Mr McCain.
New residents have streamed in from more liberals states like California while a significant number of those in the suburbs of Phoenix have turned away from the Republicans, a phenomenon seen in other states.
In many ways, Arizona is simply falling into line with its neighbouring states of Nevada and New Mexico that have been gradually tracking Democrat.
But the enthusiastic support of Mrs McCain for Mr Biden, who she endorsed in September, carried great weight.
“When you’re trying to get people who ordinarily vote Republican to vote Democrat, or vice versa, a high-profile endorsement like that of Cindy McCain, it creates a permission structure,” Rodd McLeod, an Arizona Democratic strategist, told website Politico.
Former McCain chief of staff Grant Woods said the state had been Mr Trump’s to lose. And that he did with his uncalled for insults.
“Look how close this race was in Arizona. All he had to do was show a modicum of common sense and human decency toward an American hero. He probably would have won.”
Following Mr Biden’s nabbing of Arizona’s 11 Electoral College votes, Mrs McCain released a statement seemingly designed to push Mr Trump’s buttons – particularly on the issue of voting irregularities.
“The election workers are incredibly impressive. They have worked almost literally day and night for weeks now, ensuring Arizonans could vote and then that they counted every ballot carefully.
“It has required some patience to get to the final conclusion. But, it is a conclusion that we are totally confident is legitimate.”
She said Mr Biden was defined by his love of the US and its troops “as was my husband, John”.
Finally, again without mentioning the name Trump, Mrs McCain urged a smooth transition.
“Of all people, I know what it is like to lose an election, so I am sympathetic to those who wished the election had come out another way, but I remember John’s example in 2008 of accepting the decision of the voters and moving on to the next challenge.”
Since the election, a meme has been doing the rounds on social media.
It simply shows a smiling Mr McCain and the words “I like people who don’t lose Arizona”.