US President Donald Trump and Russian President Vladimir Putin met in July 2018 in Helsinki
Trump's foreign policy faces scrutiny as former National Security Council official Alexander Vindman warns he's "giving everything" to Putin for "nothing in return" AFP

A former National Security Council official is ringing the alarm over President Trump's approach to Russian President Vladimir Putin, questioning why he's so eager to advance Moscow's agenda without any clear benefit to the U.S.

"What does Putin have on Trump that he's willing to bend over so hard to bend over backwards to, to really support Putin's agenda?" said retired Lt. Col. Alexander Vindman during an appearance on MSNBC. "It doesn't make a huge amount of sense. He's not getting anything for it right now."

Vindman, a key witness in Trump's first impeachment trial, accused Trump of "giving away the farm" in his dealings with Putin.

"I'm not sure what kind of deal he's making, where he's giving everything that his opponent wants, nothing in return," he added, according to Mediaite.

Vindman, who fled Soviet Ukraine as a child, has been in Trump's crosshairs ever since he testified against Trump's abuse of power.

Vindman labeled Trump as Putin's "useful idiot," in a September interview with The Atlantic, arguing Putin doesn't even need to use blackmail to manipulate him.

"They may or may not have dirt on him, but they don't have to use it," he said at the time. "He has aspirations to be the kind of leader that Putin is, and so he admires him."