“President Trump must clarify his statements in Helsinki on our intelligence system and Putin. It is the most serious mistake of his presidency and must be corrected— immediately.”

So said former Speaker Newt Gingrich of Donald Trump’s disappointing performance at the U.S.-Russia summit Monday.

On Tuesday the president reacted to a growing consensus in Washington that his final stop on what was a rocky foreign trip start to finish ended not with a bang but with a shocking whimper. Reading a statement before a meeting with members of Congress, Trump praised the intelligence community and said he accepted their conclusion that Russia had meddled in the 2016 election.

He then explained that he misspoke in his Helsinki comments using the word “would” instead of “wouldn’t” in talking about whether, in fact, the Russians were the culprits. As clarifications go, it’s probably the best we’re going to get.

Watch: Trump Says He ‘Misspoke’ on Russian Election Meddling

Action speaks louder …

Unfortunately, it’s likely to take more than words to correct what was a serious misstep. It’s going to take substantive action, evidence that the president’s statement reflects actual White House policy and reassurance for our allies, not just a one-time rhetorical cleanup.

The president’s aggressive diplomatic style has its advantages and disadvantages. His harsh language directed at North Korea last year delivered a summit this year. Whether it will deliver more remains to be seen.

Calling out our NATO allies for shirking their financial contributions may not be “how it’s done,” but after years of NATO members failing to pull their weight, maybe a different kind of diplomacy is just what’s needed.

Trump’s diplomatic successes and failures are fair game for debate, just as the country assesses every president’s foreign policy. But for this president, Helsinki wasn’t just a verbal stumble. In his full remarks, Trump crossed a line when he failed to give his wholehearted support to his own intelligence agencies or the Republican-led investigating committees when asked about Russian meddling in the 2016 elections.

True, we don’t know what happened between Trump and Putin behind closed doors. Perhaps the White House will yet provide a “read out” of what the two leaders actually discussed, with more detail on the tone and tenor of the president’s conversation with Putin, an ex-KGB autocrat known for a dark and deadly past.

But Trump’s grumbling comments, his ramblings about emails, servers and rogue FBI agents, and most important, his attempt to create a moral equivalency between our intel agencies and the actions of Russia, leaves most outside observers shaking their heads.

Trump seems convinced that any verbal acknowledgement of Russian interference in the election, which is settled fact at this point, chips away at the legitimacy of his 2016 victory. He wrongly conflates the mostly partisan charges of collusion with proven claims of Russian interference. The truth is, you can take a strong stand against Russian meddling while expressing skepticism toward yet unproven allegations of collusion. Trump’s trashing of the “witch hunt” need not alter our Russia policy.

Given the behavior of Democrats on the investigating committees over the past year and the over-the-top comments of their leadership, as well as former intel officials this week questioning the president’s patriotism, Trump’s suspicion is at least understandable.

As the old saying goes, “Just because you’re paranoid doesn’t mean someone isn’t following you.” And the apocalyptic post-summit pronouncements from the usual cast of media and partisan pundits with claims ranging from “Putin must have something on Trump” to “It’s the end of the republic” only add gasoline to an already raging fire.

The fact is that when AP reporter Jonathan Lemire asked Trump whether he believed his own intelligence agencies or Putin on whether the Russians meddled in the election, it wasn’t a trick question. It wasn’t even a difficult question, and it certainly shouldn’t have been a surprise to anyone.

Whatever the pre-summit preparations, the president should have instinctively known how to answer. And it wasn’t to deflect and dissemble, complain or whine.

His job was and is to defend the United States against those who would do us harm. And that is the very definition of Vladimir Putin.

Damage report

How much damage has the president done to himself? It is difficult to assess at this point. Our polling has shown consistently over the past year that people put the Russia scandal well down their list of issues they say will impact their congressional vote. In our June Winning the Issues survey, we gave voters 19 issue options and asked them to rank them in order of importance to their voting decision. “Allegations of Donald Trump’s ties to Russia” came in third from the bottom.

On the other hand, one of Trump’s strengths with voters has been his perceived tough-guy persona, the ultimate negotiator who would use a lifetime of successful deal-making to put the country back on top. There was going to be a new sheriff in town who wouldn’t take guff from anybody, and the world better get ready.

In 2016, people wanted change. That’s what Donald Trump offered and in large part has delivered, from less regulation to tax cuts that have helped produce an improving economy. But his performance in Helsinki stands in direct conflict with the larger-than-life character who strode across the political stage in 2015 and defied the predictions of the political and media establishment.

One of the most critical elements of leadership is one’s ability to inspire followers to believe not only in your vision but also in your ability to achieve that vision. When followers begin to doubt a leader’s ability to accomplish what he promised, leading becomes more difficult.

Whether Trump has damaged his image or whether Democrats can ride his mistake to a majority this fall shouldn’t be the issue. Those who support Trump’s policies have a responsibility to call him out when this kind of grievous mistake is made, regardless of the political fallout. The opposition, however, also has a responsibility to avoid the kind of destructive and dishonest hyperbole which has characterized much of the Democrats’ and media’s response, further dividing the nation.

In the end, however, it is Donald Trump who finds himself at a crucial inflection point in his presidency. He can listen to the criticism of his Helsinki comments, learn a hard lesson, rein in his shoot-from-the-hip instincts and lead — or not, and put his leadership at risk.

Perhaps Trump should take Harry Truman’s words to heart. Truman once said, “In reading the lives of great men, I found that the first victory they won was over themselves. … Self-discipline with all of them came first.”

David Winston is the president of The Winston Group and a longtime adviser to congressional Republicans. He previously served as the director of planning for House Speaker Newt Gingrich. He advises Fortune 100 companies, foundations, and nonprofit organizations on strategic planning and public policy issues, and is an election analyst for CBS News.