WASHINGTON (AP) — The former NATO chief and adviser to Ukraine's leader said Thursday that Russian President Vladimir Putin "must be laughing" at how successfully he's undermined Western democracy and exploited the Trump administration's mixed messages.

Anders Fogh Rasmussen, a former prime minister of Denmark, joined a growing a chorus of Russia critics questioning why President Donald Trump's administration failed to meet a congressionally-mandated deadline to impose new sanctions on Moscow. He said the lack of answers from the administration would be seen as a sign of weakness that plays to the Kremlin's advantage.

"President Putin must be laughing right now, because he's achieved much more than he could have ever dreamed of when it comes to undermining the credibility of Western democratic institutions," Rasmussen said in an Associated Press interview. "When he's watching the ongoing discussion here in Washington, I think it's unbelievable for him that he could achieve that much for a very modest investment in whatever he might have invested in interference in the election or whatever."

U.S. lawmakers of both parties have expressed exasperation that an Oct. 1 deadline came and went without new penalties on Russia required under a law Trump signed in August that targets individuals linked to Russia's defense and intelligence agencies. The new, congressionally-required sanctions came in addition to existing U.S. penalties on Russia for its support of separatists in eastern Ukraine and 2014 annexation of Ukraine's Crimea region.

Republican Sen. Bob Corker, the chairman of the Senate Foreign Relations Committee, has said he's urgently seeking an explanation from the administration. And in a letter to Trump this week, 20 Democratic lawmakers said the administration had done "nothing to hold Russia accountable" for interfering in the 2016 election.

"This inaction is baffling and unacceptable. It allows Russia or any other hostile actor to believe they can attack American democracy with impunity," said New York Rep. Eliot Engel and the other Democrats.

The State Department has said it's working on the sanctions while acknowledging that it missed the deadline and that lawmakers are upset. State Department spokeswoman Heather Nauert said this week that one concern was ensuring information is ready to tell businesses and U.S. allies how to avoid running afoul of the sanctions, which also require the U.S. to penalize foreign countries that do business with Russia's defense and intelligence sectors.

"As soon as we get that all put together, we'll certainly let you know," Nauert said.

U.S. officials have also cited legal hurdles to getting the sanctions in place, along with diplomatic considerations about how they may affect U.S. partners doing business with Russia.

But Rasmussen said the lack of clear communication from the administration about the exact obstacles was muddying the intended U.S. message that Russian aggression and interference won't be tolerated.

"If there are such legal complications, the administration should as soon as possible engage with Congress to solve those problems, at least inform Congress about those obstacles," Rasmussen said. "Otherwise, the administration will leave the suspicion it's because of a hesitation."

Rasmussen, who began advising Ukrainian President Petro Poroshenko earlier this year, called in the interview for the U.S. to provide lethal, defensive weaponry to Ukraine's forces. That move has been under consideration for years, including under former President Barack Obama. The U.S. has not yet taken the step despite floating the possibility publicly on several occasions.

"So far, nothing has happened from the administration side," Rasmussen said. Still, he said just the threat of U.S. weapons potentially flowing to the Ukrainians had affected Putin's deliberations about Ukraine in a positive way. He said he believed Putin's recent proposal to send U.N. peacekeepers to eastern Ukraine reflected the Russian leader's "attempt to find a way out of all of this."

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