When Donald Trump proclaimed that “maybe there was no hacking” by Russia, the candidate was flatly rejecting the consensus of the American intelligence community — and that worries the ranking member of the House Permanent Select Committee on Intelligence.

“If he was willing to disregard the intelligence community and contradict it to his benefit during the campaign, will he do so as president?” said Rep. Adam Schiff, D-Calif. “Time alone will tell, but there are, I think, grave concerns about that.”

Schiff, who spoke Thursday at the Defense One Summit in Washington, had just come from a hearing on Capitol Hill at which Director of National Intelligence James Clapper reiterated that the IC believes that Russia meddled in the recent American election.

“There is substantial concern about whether he respects, one, the process and, two, the personnel of the IC, especially when they tell him things that he doesn’t want to hear,” the lawmaker said. “As DNI Clapper said today, there is truly no question that Russia meddled.”

Should the U.S. hack back at Russia? Schiff said the U.S. must show that this is unacceptable and will draw a response. If Trump goes soft on this issue, he said, he will soon find the Russians hacking and distributing documents from his own party and administration.

“The one thing that gets Russian attention, frankly, is the sanctions,” he said. “We shouldn’t be talking about doing away with sanctions, we should be talking about adding sanctions.”

Asked about the reported appointment of retired Lt. Gen. Michael Flynn as Trump’s national security advisor, Schiff began by praising Flynn’s work as head of the Defense Intelligence Agency with Gen. Stan McChrystal in Afghanistan.

“But I do have concerns about him as national security advisor, to be candid,” he said, starting with Flynn’s ties to Russia.

As someone who views Russia and its president with great anxiety, Schiff said, “It concerns me a great deal that the president-elect may be getting advice that reinforces his view of Putin.”

Moreover, he said, Flynn has, in Congressional hearings, demonstrated a tendency to “shoot from the hip.”

“Ideally, the president, who strikes me as having something of an impulsive personality, would have someone smoothing out those impulses,” but Flynn seems to share that temperament, he said.

Schiff also noted Flynn’s recent op-ed suggesting that Muhammed Fethullah Gülen, a prominent opponent of Turkish leader Recep Tayyip Erdogan, should be extradited to Turkey, where he would face possible imprisonment on political grounds.

He was asked about Trump’s suggestions that his administration may end U.S. support for Syrian rebels: What if Trump and Putin forge a solution that allows Assad to stay in power?

“I think the civil war churns on,” Schiff said. “As long as Assad is in power, that war will go on. It may take the form of a large-scale insurgency instead of a group that holds territory, but it will churn on...I think there will be a reputational cost to the United States, and further aggrandize Iran and Russia.”