"I've been optimistic in what I've seen, and it started frankly on Election Night when he came out and said it's time to unite, not just the party but the country. And I'm like, 'Wow that's good to hear,'" Kinzinger told CNN commentator Mary Katherine Ham on Monday.
It's a switch for Kinzinger, who said in August that he could not support Trump as the GOP presidential nominee
because, "I'm an American before I'm a Republican." Now Kinzinger says he will "support the President-elect as often as possible, and I'll still oppose him when I must."
The Illinois congressman highlighted the confirmation challenges Trump's secretary of state pick Exxon CEO Rex Tillerson could face because of his Russian connections.
Kinzinger mentioned GOP Sens. John McCain, Marco Rubio and Lindsey Graham, who are skeptical of Russia and have expressed concerns about Tillerson.
"This will be flushed out in the hearing process. And I think if it's shown, 'Hey we want to be pals with Russia,' he's going to have a hard time getting confirmed," Kinzinger said.
Despite skepticism of Russia from members of his own party, the GOP congressman sought to downplay the threat of Russia against the United States.
"This isn't the old Soviet Union. This isn't the old, bipolar world where we're up against this red Russian wall. This is a country the size of Italy," Kinzinger said. "Now they have a powerful nuclear force obviously, but even in Syria, half of their planes are grounded because they don't have the stuff to fix them. So this idea that we're so fearful of starting a conflict with Russia, Russia is way more fearful of starting a conflict with us. We've just put no walls to stop them from moving forward."
Kinzinger acknowledged the seriousness of Russia's alleged hacking role during the US presidential election, but cautioned Democrats should not use it to delegitimize Trump's win.
"I think in a bipartisan way we need to figure out what they did, and how to prevent it from happening in the future," he said. "But they are trying to take it one step further, and say the Russians made Donald Trump president. And what you've done in that is now you've put both sides in their corner and we're not going to get to a real solution here."
The congressman said he's also open to Trump's use of social media.
"If it's something that can come out, like, 'Hey here's a new policy position we're announcing, something we want to communicate to the people,' it can be very effective," he said.
"Keep in mind every new president has done something different than the president before. This new one is going to be very different."
Kinzinger, who is an Iraq and Afghanistan war veteran, defended Trump's selection of generals for high-ranking national security positions, and praised his pick of retired Gen. James Mattis as secretary of defense.
"I think it's going to be really good because there's a lot of bureaucracy in the Pentagon, there's a lot of waste, there's a lot of problems there, and there's nobody like a general who has dealt with it, who knows where the skeletons are buried, that can come in and do something about it," Kinzinger said.
"We know how to make the Pentagon better, and I think that's a role that Mattis is going to play to great effect."