There is "no good explanation" for President Donald Trump's decision to call Russian President Vladimir Putin and congratulate him for his election win, Sen. Chris Coons said Wednesday.

"I'm also deeply concerned and think many of my colleagues Republicans and Democrats see clearly that there is no good answer," the Delaware Democrat told MSNBC's "Morning Joe" program. "He called President Putin and congratulated him on his election and makes no mention of the pressing national security concerns of this country, there is no good explanation for that."

The United States, Coons continued, is a "significantly more powerful country than Russia" and needs to lead with its values.

"He's not making America great again," said Coons. "He's taking us back to the isolationism of 70 years ago."

Coons on Wednesday also urged action for a bill to protect special counsel Robert Mueller from being fired from the probe into Russian activities.

"There were some strong statements from a number of Republican senators, [Arizona Sen.] Jeff Flake in particular," said Coons, adding that Sen. John McCain, R-Arizona also put out a strong statement and both House Speaker Paul Ryan and Senate Majority Leader Mitch McConnell both have said Mueller should be able to complete his investigation.

"I think we need to do more," said Coons. "Anyone who thinks special counsel Robert Mueller isn't in imminent danger of being fired isn't paying attention. Just look at your phones. The tweets coming out from President Trump this morning make it clear that he is rattling the cage and threatening to fire him."

However, it's been "frustratingly difficult" to get even Republicans who agree that it would be bad for Mueller to be fired to co-sponsor a bill to protect him.

"They say, 'that's not going to happen. I've gotten reassurances from the White House it's not going to happen,'" said Coons. "My mom used to say 'an ounce of prevention is worth a pound of cure.'"