Trump comes out ahead, 46-41, with Libertarian Gary Johnson following at 5 percent and Green Party candidate Jill Stein at 2 percent.
When Monmouth last polled Missouri in mid-August, Trump led by one point, 44-43, with Johnson at 8 percent and Stein at 1 percent. But as recently as late September, polling showed Trump with a substantial advantage, leading by nine points in a CBS/YouGov poll and 10 points in a Remington Research poll.
The Monmouth University poll was conducted Oct. 9-11 among 406 likely Missouri voters, with a margin of error of plus or minus 4.9 percent.
TPM's PollTracker Average for the general election in Missouri shows Trump leading Clinton, 45.9 to 41.4.