And then, of course, there's President Donald Trump, who in his tweets, just hours after the London Bridge attack, criticized Khan, alleging he was downplaying the terrorist threat.
But on the streets of multicultural London, Khan is getting good marks for how he has handled the aftermath of the attacks.
The son of a Pakistani immigrant who worked as a bus driver, from the Tooting borough of London, Khan has been a steady fixture on television screens and social media since the attack, channeling the city's anger, sorrow and defiance.
Under dark clouds at a vigil at Potters Fields Park on Monday, Khan directly addressed who he is and where he comes from.
"As a proud and patriotic British Muslim, I say this - you cannot commit these disgusting acts in my name. Your perverse ideology has nothing to do with true values of Islam, and you will never succeed in dividing our city."
The line got the loudest applause.
In interviews, tweets and remarks, Khan called the Saturday night vehicular and knife attacks at London Bridge and the nearby Borough Market by turns evil, sick, hideous and barbaric. Eight people were killed and dozens wounded. The three attackers, all Muslims who lived in east London at least recently, were shot dead by police during their assault.
At the vigil beside City Hall, Khan warned terrorists, "We will defeat you. You will not win."
Tony Travers, an expert on local government at the London School of Economics, said of Khan, "He was popular before the attacks, and he's probably more popular now."
Khan prays often and does not drink alcohol.
"He is devout in a religious sense. He doesn't wear it on his sleeve. Rather, he uses it to understand other people and to respect their religions or those who have no religion. Plus, he's a social liberal. So he's a perfect fit for London, with its large numbers of Polish Catholics, its Jewish population and Hindus, Sikhs, Muslims, Anglicans and on and on," Travers said.
During his election campaign last year, Khan described himself to the New Statesman this way: "I'm a Londoner, I'm British, I'm English, I'm of Asian origin, of Pakistani heritage, I'm a dad, I'm a husband, I'm a long-suffering Liverpool fan, I'm Labour, I'm Fabian, and I'm Muslim."
But he was criticized during the campaign by his Conservative Party opponent, Zac Goldsmith, who said Khan had given "platforms and oxygen and cover and excuses" to extremists.
Khan accused his rival of "Donald Trump-style" antics.
Travers said Khan performed in recent days as Londoners expected - repeating a steady reprise of "keep calm and carry on," the line used in 1939 motivational posters distributed by the British government on the eve of World War II.
"He's shown good, inclusive leadership. He is the mayor for all who happen to be Muslim, and I think he has, more than some Western leaders, shown that he is, in fact, for all the people," said Ashfaq Siddique, secretary of the al-Madina Mosque in Barking, near where at least one of the London attackers lived.
Kenny Norcross, a vendor in Barking, agreed. "No complaints. He's done us proud."
Khan's statements after the attack mirrored those by Prime Minister Theresa May, the Conservative Party leader in the midst of a suddenly competitive election campaign.
After Trump's tweets, May came out in support of Khan, saying she believed the London mayor was doing an "excellent job." May said politics should be put to the side to deal with the terrorist threat.
Still, Khan is a star in the Labour Party - and though he is not a big booster of May's main challenger, Jeremy Corbyn, Khan has played off the London Bridge attack to warn that if the Conservative Party wins the election Thursday, they would likely slash budgets for front-line police officers.
"Cuts on this scale would make it harder to foil future terrorist attacks on our city - and as the mayor of London, I'm simply not willing to stand by and let that happen," Khan said.
In the hours after the rampage, Trump wrote in a tweet, "At least 7 dead and 48 wounded in terror attack and Mayor of London says there is 'no reason to be alarmed!' "
After news reports stressed that Khan's comments were an advisory to citizens not to be alarmed by the heightened presence of police on London streets, Trump followed with another tweet: "Pathetic excuse by London Mayor Sadiq Khan who had to think fast on his 'no reason to be alarmed' statement. MSM is working hard to sell it!"
"I think Donald Trump was wrong in the things he has said about Sadiq Khan," May said.
Trump and Khan have a history. When Trump was running for president, Khan predicted that Trump's populist rhetoric would fail.
Since Trump's win, Khan has argued against inviting the American president for a state visit to Britain, calling it "inappropriate" because of Trump's proposed travel ban for visitors from several Muslim-majority nations.
Khan told the Associated Press this week that there are "literally millions and millions of Muslims around the world who love America."
"They love Britain, they want to come here to study, to be a tourist, to start up a business, to work, to learn. Why would you want to stop them coming?" Khan said.
Khan has mostly declined to reply to Trump. "I don't know how to tell you this, but I really don't care," the mayor told the AP.
(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)
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