Depends what you mean by internationalism.
Nationalism is putting the interests of you nation first. If you define Internationalism as NOT doing that, then indeed they are opposites.
Trump wants to limit immigration to benefit citizens of the American Nation.
American citizens by definition have a right to expect that national policy will be crafted for the benefit of national citizens.
Anyone that thinks the needs of the caravan for say, some reason off "fairness" or "charity" is more important that the self interests of Americans, or the Right of Americans to define America,
is being an Internationalist and opposing the very bedrock of Nationalism.
The definition of internationalism that I found was a branch of communism
What SHOULD happen, in my Nationalist opinion, is that President Trump should demand that Mexico stops the caravan way before it gets here.
Mexico, looking to their self interest of keeping good relations with their very powerful neighbor, does so, with as much force as needed.
America is grateful for Mexico being a good neighbor and increased co-operation follows.
In this scenario, both NATIONAL leaders are rightfully NATIONALISTIC, in crafting policy that serves the interests of their nation,
WHILE co-operating with each other to shared mutual advantage.
In a sane world, that is what would happen.