WASHINGTON — U.S. Sens. Michael Bennet and Cory Gardner of Colorado agree that Michael Flynn was right to resign his post as national security adviser after it was revealed that Flynn spoke with a Russian ambassador about U.S. sanctions on Russia and later lied about it.

But the lawmakers disagree somewhat on what should come next.

Bennet, a Democrat, has joined with fellow party members in calling for a new investigation into Flynn’s conversation — and who in the nascent administration knew about it.

“General Flynn’s resignation is not enough,” Bennet said in statement. “The American people deserve the full story, including when the White House became aware of General Flynn’s communications and whether anyone directed him to discuss our sanctions policy with Russian officials.”

Gardner, in an interview, didn’t go as far as Bennet and said he wants the FBI — which reportedly interviewed Flynn — to finish its work, or brief lawmakers, before Congress launches something new.

But the Colorado Republican didn’t rule out an investigation from Capitol Hill either. Senate Majority Leader Mitch McConnell on Tuesday said he expects lawmakers on the intelligence committee to examine the Flynn situation as they look at Russian interference more broadly.

And Gardner continued to push President Donald Trump to take a stronger position with Russia than what the new commander in chief has done so far.

“When it comes to Russia, we want to make sure it’s clear that the administration lay out lines that we will not cross,” said Gardner, citing Moscow’s actions in Syria, Ukraine and global cyberattacks, “including the U.S. during the election.”

He added: “It will be a very good outcome if the president starts taking a firm line on Russia.”

The admonishment follows a series of nudges Gardner has directed toward the White House in recent weeks.

Last week, Gardner and several of his Republican colleagues urged Trump to take a tougher stance on Russia.

The letter he co-signed asks Trump keep in place sanctions the U.S. has levied against Moscow — penalties Trump in January suggested lifting. They argue that Russia’s actions toward Ukraine, including its 2014 annexation of Crimea, are reasons to stay vigilant.

“The administration should maintain the current U.S. sanctions regime against Russia and Russian entities — and to impose new sanctions as necessary and merited by Russian behavior –unless Ukraine’s control over Crimea is restored, Russia fully respects the Minsk agreements, and ceases all efforts to undermine Ukraine’s sovereignty,” wrote Gardner and his colleagues.

Gardner also has pushed back against Trump’s criticism of NATO, the long-standing defense alliance the U.S. shares with much of western Europe.

Trump previously has criticized NATO as “obsolete” and raised concerns about the financial commitment of the U.S. compared with other members. More recently, Trump has pledged support for NATO.

A bipartisan resolution co-authored last week by Gardner asks the U.S. to “strengthen its commitments” to NATO and — in a nod to Trump’s criticism — ask that member nations “fulfill their pledge to invest at least 2 percent of gross domestic product on defense spending.”

Gardner, too, has signed onto legislation that would impose new sanctions on Russia in response to the cyberattacks it committed during the 2016 election, as well as its actions in Ukraine and Syria.