Taken from the Guardian article linked above - I think just about sums it up
Another Republican who spoke in support of Trump’s comments was Florida US senator Marco Rubio. Rubio sought to downplay the meaning of Trump’s remarks, made two days after former Fox News host and Trump ally Tucker Carlson conducted a lengthy, virtually free-ride interview with Putin.
“Trump was talking about a story that happened in the past when he was president,” Rubio told CNN. “He didn’t pull us out of Nato, and American troops are stationed throughout Europe then as they are today.”
“Donald Trump is telling a story,” Rubio continued. “He’s not a member of the council on foreign relations. He doesn’t talk like a traditional politician, and you’d think people could have figured that out by now. He said Nato was broke or busted until he took over because people weren’t paying their dues and he used leverage to get them to step up to the plate.”