Ex-FBI chief James Comey testified Thursday that President Trump’s son-in-law, Jared Kushner, would have given Russia’s spies a boost if he had succeeded in setting up “back-channel” communications with the Kremlin.

“The primary risk is obvious. You spare the Russians the cost and effort of having to break into our communication by using theirs and so make it a whole lot easier for them to capture all of your conversations and to use those to the benefit of Russia against the United States,” he told the Senate intelligence committee.

Kushner, one of Trump’s top advisers, has been named a person of interest in special counsel Robert Mueller’s criminal probe into Russia’s meddling in the presidential election.

Kushner in December allegedly approached Russian US Ambassador Sergey Kislyak and inquired about establishing the line of communications using equipment in a Russian diplomatic facility.

Under questioning from Sen. Martin Heinrich (D-NM), Comey said he would not comment more specifically “in an open setting” because the matter remained under investigation.

Kushner failed to disclose his meetings with Kislyak, and that he also met with the head of a shady Russian state-owned bank.

The Trump administration has downplayed the revelations, saying it was common for government officials to arrange back-channel communications — even though Trump had not been sworn in at the time, meaning his son-in-law had no official role.

Comey also said that Kushner was present at a Feb. 14 Oval Office meeting for a counterterrorism briefing.

As the meeting came to an end, Trump asked everyone to leave so that he could have a private conversation with Comey.

Both Attorney General Jeff Sessions and Kushner, the husband of Trump’s daughter Ivanka, stuck around until the president insisted that they move along.

“My sense was the attorney general knew he shouldn’t be leaving, which is why he was lingering,” Comey said about Sessions, while suggesting that Kushner lingered for the same reason.