President Trump on Thursday at a campaign rally in Montana for Republican Senate candidate Matt Rosendale said he would tell NATO members on Monday, “You gotta start paying your bills.”

“I’m going to tell NATO, ‘You gotta start paying your bills. The United States is not going to take care of everything,'” he said to loud cheering from the crowd in Great Falls, Montana.

Trump is headed to Brussels, the headquarters of NATO in Belgium on Monday, where he is expected to call on members of the security alliance to increase their own defense spending.

NATO members in 2002 pledged to meet a benchmark of defense spending of at least two percent of their gross domestic product. Today, four of 29 members meet that benchmark.

In 2014, NATO-member heads of state agreed to meet the two percent benchmark by 2024, but only 16 have plans to achieve that goal.

Germany, a member of NATO and the fourth largest economy in the world, only pays 1.24 percent of their GDP on defense, and has a plan to meet only 1.5 percent by 2024. The U.S. pays 3.58 percent of its GDP on defense, and pays the most into the security alliance.

NATO was established after World War II to help rebuild Europe and stave off Russian aggression there. NATO has since been involved in the Balkan Wars, and joined the U.S. in the Afghanistan War in the aftermath of the 9-11 attacks, but the U.S. has footed most of the bills.

Trump criticized NATO members for not paying more for their own defense, while exacting uneven trade terms with the U.S. He said:

We’re paying for anywhere from 70 to 90 percent to protect Europe and that’s fine. Of course, they kill us on trade, they kill us on other things. They make it impossible to do business in Europe. And they come in and they sell their Mercedes and their BMWs to us. So we have $151 billion dollars in trade deficits with the EU. And on top of that they kill us with NATO.

He focused most of his vitriol against Germany and German Chancellor Angela Merkel:

They kill us. So we pay four percent of a huge GDP. And Germany, Germany — which is the biggest country of the EU…Germany pays 1 percent. One percent. And I said, ‘You know Angela, I can’t guarantee it, but we’re protecting you, and it means a lot more to you than protecting us because I don’t know how much protection we get by protecting you.

“They go out and they make a gas deal — oil and gas from Russia, where they pay billions and millions of dollars to Russia, OK? So, they want to protect against Russia, yet they pay billions of dollars to Russia, and we’re the schmucks that are paying for the whole thing.”

Trump said that since he took office, almost $33 billion dollars more is projected to be paid by NATO members.

“But it’s not enough,” he said. He said NATO Secretary General Jens Stoltenberg told him that when he took office, NATO members began increasing their spending.

Stoltenberg, he said, “is Trump’s biggest fan. He said …’When you came in and started talking, it went like a rocket ship.'”

Trump also touched on his upcoming summit with Russian President Vladimir Putin, after meeting with NATO member countries. He mocked those who have criticized him for wanting to get along with Russia, a nuclear power state.

“Getting along with Russia and getting along with China is a good thing — it’s not a bad thing,” he said, pointing out he has only increased U.S. military spending. Russia and China “would rather have Hillary,” he said.

He said his goal was to make the military “so powerful and so strong that nobody wants to play games.”

“Hopefully we’ll never have to use it,” he said.