Two theories about the polling this cycle
1) Trump is screwed and he is gonna be washed out in a giant blue tsunami
2) Polling this year is heavily favoring the dems and the actual results will be much better for Trump
"We Ask America" is an R-friendly pollster. To be sure, Missouri gets polled rarely, and lacking a Senate race and not having been close in a Presidential race since 2008 one can easily see why Missouri attracts little attention by pollsters this year. If you dislike the result of a certain poll, then wait for another to refute or corroborate it.
Donald Trump has done very well in the Mountain South, as have McCain in 2008, Romney in 2012, and of course Trump in 2016. Missouri is in part Deep South (the flat southeastern part of the state, part Rust Belt (Kansas City and St. Louis), in part an extension of southern Iowa, eastern Nebraska, or western Illinois (the I-70 corridor and everything to the north except Greater KC and Greater St. Louis), and the Ozarks. I have been in the Ozarks and Appalachia; they look much alike and were settled by much the same people. The Missouri Ozarks are practically impossible to distinguish from West Virginia.
Yes, I consider this poll hard to believe.
On the other hand --
Donald Trump is failing catastrophically as President. He got away with much before COVID-19 struck America -- but that is over. President Trump now has a political disaster on par with a military catastrophe.
Strange things happen in a wave election against an incumbent President. What? Carter is behind in Massachusetts? That just can't be right!
Yes, Carter actually lost Massachusetts in a re-election bid. The impossible seemed to happen.