It may be only a coincidence that Trump authorized the bombing of the Syrian military base exactly when China’s Xi Jinping is visiting him in the US. But Trump is known for trying to show strength, almost in a provocative way, during meetings with other leaders. Do you remember the handshakes? Or the lack of handshakes?
I think it is reasonable to believe that the recent intervention in Syria also aimed at coercing Xi Jinping to make concessions during the tough negotiations that are set to take place these days. Also, Donald Trump might try to prove Xi Jinping that the US is ready to act unilaterally in case an agreement on North Korea is not reached.
On the other hand, it pays off for Trump to bomb Syria now. He shows some strength after the recent defeat with Obamacare.
After bombings Syrian, it is likely that Trump will get a taste of foreign policy, and he will be more involved in international issues. He will understand that “America First” also means to protect its interests abroad. Slowly but surely Trump will start to act and think exactly like the establishment he seemed to despise so much.