"Well, take a look at what we've done too. We've made a lot of mistakes. I've been against the war in Iraq from the beginning," Trump said during an interview with Fox News.
"A lot of mistakes, OK, but a lot of people were killed. So a lot of killers around, believe me," said the US President when told that the Russian President Vladimir Putin is a "killer".
Trump said he would like to co-operate with the Russians in the fight against ISIS.
He also said that he respects Putin, but this does not mean that the two would get along.
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"Well, I respect a lot of people but that doesn't mean I'm going to get along with them. He's a leader of his country. I say it's better to get along with Russia than not. And if Russia helps us in the fight against ISIS, which is a major fight, and Islamic terrorism all over the world...," Trump said.
The comment has drew criticism from his political opponents, who see it as him comparing the US with Russia.
"Equating our country with an authoritarian, murderous regime is outrageous and reprehensible, even for Mr Trump. All elected officials in the United States have a responsibility to speak up against the President's dangerous rhetoric," said Senator Ben Cardin, Ranking member of the Senate Foreign Relations Committee.
Cardin said Trump made clear he does not believe in America's exceptionalism when he equated the United States to Vladimir Putin and his murderous regime.
Political opponents and independent journalists in Russia have been attacked, jailed, and killed under Putin's regime, he said.
Democratic Leader in the House Nancy Pelosi also accused Trump for being soft on Russia.
"I want to know what the Russians have on Donald Trump," Pelosi told NBC News in an interview.
Trump's respect for Putin was a familiar trope during presidential election which the major US intelligence agencies believe Russian intelligence sought to influence on Trump's behalf. Such beliefs prompted a fierce split between Trump and the intelligence community that has not yet healed.