Speaking to reporters, Mr Trump said Russia had "violated" the 1987 Intermediate-Range Nuclear Forces (INF) treaty.
The deal banned ground-launched medium-range missiles, with a range of between 500 and 5,500km (310-3,400 miles).
The US would not let Russia "go out and do weapons [while] we're not allowed to", Mr Trump said.
"I don't know why President [Barack] Obama didn't negotiate or pull out," the president said after a campaign rally in Nevada. "They've been violating it for many years."