A presidential historian who served in both the Bush and Obama administrations said Thursday that former President Reagan would be "appalled" by President TrumpDonald John TrumpMost Americans break with Trump on Ukraine, but just 45 percent think he should be removed: poll Judge orders Democrats to give notice if they request Trump's NY tax returns Trump's doctor issues letter addressing 'speculation' about visit to Walter Reed MORE's rhetoric toward Russia's Vladimir Putin.

Walter Isaacson, who served as chairman of the Broadcasting Board of Governors for three years under former President Obama, told MSNBC's "Morning Joe" that he was disgusted to see Republican senators seeking a meeting with the Russian leader on July 4 while America celebrated Independence Day.

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"When I saw an entire Republican-only delegation there in Moscow on the Fourth of July saying we're talking to Putin, I realized that this administration has enabled them to take pages out of Putin's playbook and serve his purpose," Isaacson said.

"That is worse than enabling [Nicaraguan president] Danny Ortega," Isaacson continued. "I mean, Ronald Reagan would be appalled."

Isaacson added that Trump's administration was spurring dictators around the world to "push back" against international law.

"What's happening now is this push back on the rule of law by authoritarian leaders around the world enabled, empowered, and led by Donald Trump," he said.

Trump has faced criticism from Democrats and some Republicans for pursuing relationships with world leaders such as the Philippines President Rodrigo Duterte and China's Xi Jinping without broaching the subject of their human rights records, a break from past U.S. presidents.

Sen. Bernie SandersBernie SandersRahm Emanuel: Bloomberg, Patrick entering race will allow Democrats to have 'ideas primary' Feehery: Pivoting to infrastructure could help heal post-impeachment wounds Jayapal hits back at Biden on marijuana 'prohibition' MORE (I-Vt.) hammered the president last year after Trump said he believed a claim from Putin that Russia was not involved in efforts to sow discord and misinformation during the 2016 U.S. presidential election.

“Well, at least Trump is consistent. Abroad, he has never met a leader of an authoritarian nation (Russia, China, Saudi Arabia, Philippines) that he hasn't liked,” Sanders tweeted. “At home he shows contempt for the U.S. Constitution and democracy.”