CLEVELAND, Ohio—Rep. Adam Kinzinger (R., Ill.) on Wednesday expressed concern about Donald Trump’s dismissive tone on NATO and friendliness toward Russian President Vladimir Putin.

Kinzinger, who has hesitated to support Trump and criticized the candidate’s foreign policy, told the Washington Free Beacon in a brief interview at the Republican National Convention that he believes Trump’s characterization of NATO as obsolete is evidence of his "lack of understanding" of the crucial alliance.

Trump has repeatedly questioned NATO’s relevance and accused member countries of "not paying their fair share," suggesting that countries that cannot pay should be forced out of the alliance.

"Many countries are not paying their fair share. That means we are protecting them, giving them military protection," Trump said at a Wisconsin rally in April. "They’re ripping off the United States. And you know what we do? Nothing. Either they have to pay up for past deficiencies or they have to get out. And if it breaks up NATO, it breaks up NATO."

"I think it’s a lack of understanding of NATO," Kinzinger said on Wednesday morning following a forum on national security. "NATO is responsible for the fall of the Soviet Union; it invoked Article V after 9/11 after we were attacked. If we want to stop ‘go it alone’ foreign policy, we have to have allies, and what better allies [are there] than NATO?"

"We criticize President Obama for saying our allies don’t trust us and our enemies don’t fear us," Kinzinger continued. "But when you say things like ‘we’re going to get out of NATO,’ our allies aren’t going to trust us and our enemies aren’t going to fear us. It just happens to be a Republican [saying it], not a Democrat."

Kinzinger said Trump was right to suggest that America’s NATO allies should be spending more on defense. Currently, only five of 28 NATO member states are meeting NATO’s defense spending guidelines.

Kinzinger, an Air Force veteran who served in Iraq and Afghanistan, criticized Trump’s foreign policy positions only hours after the candidate was formally declared the Republican Party’s nominee at the convention on Tuesday evening, over the opposition of some delegates. Kinzinger said he would have more confidence in a Trump administration if the nominee surrounded himself with credible foreign policy experts.

During a panel discussion hosted by the Washington Post, Kinzinger questioned Trump for describing Putin as a "strong leader" and for suggesting he would have a poor relationship with former British Prime Minister David Cameron after the leader criticized Trump’s proposed ban on Muslims entering the United States.

"When you talk about loving strong men, you talk about how great Russia is, and you attack David Cameron because he said something mean about you, that’s concerning," Kinzinger explained.

When asked to reveal his most pressing question for Trump on foreign policy or national security, Kinzinger replied, "I would want some real answers on Russia."

"I would want to know his real opinion on Vladimir Putin and Russia, and I think getting to the bottom of that opens up to what your real belief is on foreign policy," Kinzinger said.

Trump’s friendliness toward Putin has been the subject of scrutiny. Several Trump loyalists, including campaign chairman Paul Manafort and foreign policy advisers Carter Page and retired Lt. Gen. Michael Flynn, have ties to the Russian government.

Convention delegates on Monday accepted a Republican platform that contained softened language about what the United States should do to oppose Russian aggression in Ukraine. According to a report in the Washington Post, the stance on Ukraine was weakened at the behest of the Trump campaign. Trump allies orchestrated an effort to strip a section from the platform calling for the United States to provide lethal defensive weapons to Ukraine, resulting in language similar to the Obama administration’s policy toward Ukraine.

"If in fact Trump’s folks are behind that, that’s extremely concerning to me," Kinzinger told the Free Beacon. "I think the best way to prevent us getting involved in the war and the best way to push back against Russia is to give the Ukrainians what they need to defend their sovereign territory that we said we would help defend. If that’s in fact the case, that’s really disturbing."

Carter Page, who has connections to Russian gas giant Gazprom, has criticized U.S. policy toward Ukraine and accused NATO of "meddling in the affairs of Eastern Europe." At a recent speech in Moscow, Page knocked Western powers for what he called a hypocritical focus on "democratization, inequality, corruption, and regime change" and praised the foreign policies of Russia and China.

President Obama has come under fire for resisting recommendations from military leaders and officials to give lethal weapons to Ukraine. While Republicans were mostly united in support of arming Ukraine after Russia’s annexation of Crimea two years ago, this year’s platform calls only for "appropriate assistance" to the Ukrainians.

"We support maintaining and, if warranted, increasing sanctions, together with our allies, against Russia unless and until Ukraine’s sovereignty and territorial integrity are fully restored," the platform states. "We also support providing appropriate assistance to the armed forces of Ukraine and greater coordination with NATO defense planning."

Sen. Rob Portman (R., Ohio), who supports Trump, expressed concern over the platform when pressed by a reporter at an event outside the convention on Tuesday.

"I’m concerned about that. We need to stand up for Ukraine," said Portman, who faces reelection this year. "They’ve made their decision to be with the West, to be with us, to be with the EU, to seek freedom and liberty. As we hold ourselves out as not just the world’s longest democracy but one that promotes freedom around the world, we need to stand with our friends."