Nicholas Burns, a veteran U.S. diplomat and current Harvard professor, fired back at President Trump Donald John TrumpUS reimposes UN sanctions on Iran amid increasing tensions Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Trump supporters chant 'Fill that seat' at North Carolina rally MORE's claim on Wednesday that the Obama administration failed to adequately address Russian efforts to meddle in the 2016 election.

"Obama expelled 35 Russian diplomats, closed two Russian compounds in U.S., sanctioned Moscow and alerted us to its conspiracy against our election," Burns, who served in both Democratic and Republican administrations, tweeted to Trump.

"You haven’t even implemented sanctions Congress voted. And you’ve never criticized Putin," he added. "You haven’t defended us."

Obama expelled 35 Russian diplomats, closed two Russian compounds in U.S., sanctioned Moscow and alerted us to its conspiracy against our election. You haven’t even implemented sanctions Congress voted. And you’ve never criticized Putin. You haven’t defended us. https://t.co/QLqqrgIZjy — Nicholas Burns (@RNicholasBurns) February 21, 2018

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Trump has repeatedly blamed former President Obama for not doing more to combat Moscow's efforts to disrupt and influence the presidential election, and has insisted that he is "much tougher" on Russia than his predecessor was.

In a Wednesday morning tweet, Trump questioned why the Obama administration is not the subject of special counsel Robert Mueller Robert (Bob) MuellerCNN's Toobin warns McCabe is in 'perilous condition' with emboldened Trump CNN anchor rips Trump over Stone while evoking Clinton-Lynch tarmac meeting The Hill's 12:30 Report: New Hampshire fallout MORE's investigation into Russian meddling efforts, and appeared to suggest that Attorney General Jeff Sessions Jefferson (Jeff) Beauregard SessionsTrump's policies on refugees are as simple as ABCs Ocasio-Cortez, Velázquez call for convention to decide Puerto Rico status White House officials voted by show of hands on 2018 family separations: report MORE should open an investigation into Democrats.

Media reports have indicated that Obama was slow to act on intelligence that the Russians had sought to sow discord in the U.S. election.

But in the weeks before he left office, Obama expelled 35 Russian diplomats from Washington and ordered the closure of two Russian diplomatic compounds. He also slapped new sanctions on Russian agencies and individuals suspected of cyberattacks in the U.S.

Trump has faced criticism from Democrats and some Republicans for his reluctance to take a harder line on Russia. The Trump administration still has not implemented sanctions passed by Congress last year.

The administration has argued that the mere threat of sanctions has acted as a deterrent for Russia, and that there is not yet a need to implement the penalties.