Just before leaving for Poland on the first stop of a three day trip to Europe, President Donald Trump issued a straightforward reminder to leaders of the G20 nations, again raising the issue of trade deals involving the United States, and also rebuking China for not doing enough to rein in the nuclear weapons program of North Korea.

Trade has long been one of the more important issues for Mr. Trump, who used it during the campaign to argue that American jobs were being sacrificed by leaders of both parties, by agreeing to trade deals that were tilted in favor of other countries.

Just before getting on Air Force One, the President made clear that he was ready to again bring up trade again with other world leaders.

The reaction to the Trump tweets was immediate in Europe.

"Trump is tweeting on trade/protectionism ahead of the G20 meeting this weekend," said the research arm of Danske Bank, a major European financial group.

While no trade agreements are expected to be announced that involve the United States, Japan and the EU are reportedly ready to announce their own trade deal - which was being characterized as push against possible protectionist moves by the Trump Administration.

The President was also sending messages to China as well, both on trade and on North Korea.

Mr. Trump has made no bones about his hopes that the Chinese government would use its influence to rein in the nuclear ambitions of the Pyongyang regime; instead, more and more missile tests have taken place in recent days, with Mr. Trump giving off more bellicose responses about those military moves.

Before leaving the White House, the President again made clear that he doesn't think China has pulled all the necessary levers to get tough on the North.

"So much for China working with us - but we had to give it a try!" the President tweeted.

Mr. Trump was first flying to Poland, where he will give a speech on Thursday in Warsaw. The President will then travel to Germany for the G20 Summit, and return this weekend to the U.S.

The G20 encompasses what the group describes as "the world's largest advanced and emerging economies; that includes not only the U.S., but also Argentina, Australia, Brazil, Canada, China, France, Germany, India, Indonesia, Italy, Japan, South Korea, Mexico, Russia, Saudi Arabia, South Africa, Turkey, United Kingdom, and the European Union.

This is the second foreign trip for President Trump. He will also go back to Europe next week to visit France around their national holiday of Bastille Day.