Republican presidential Donald Trump made a campaign stop in Milwaukee, Wisconsin on Sunday just before Tuesday's primary vote and told voters he doesn't agree with letting Syrian refugees into the United States."We have no idea where they come from. They could be ISIS, and they might not be, but they could be ISIS. Did you ever notice the migration? There are so many young strong men. Where are the women and children?" Trump said."And I said don't let them in, we can't let them in. We'll build a safe zone, we'll build a free zone... We'll get the Gulf states to pay, cuz I don't want to pay," Trump added.Tuesday could be a turning point in the Republican nomination race, when Wisconsin hosts its nominating contest.Trump trails leading rival Cruz in the Upper Midwestern state. A Cruz win would make it harder for Trump to reach the magic number of 1,237 delegates needed to secure the nomination before the Republican national convention in July.The winner will get to claim all of Wisconsin's 42 delegates.