You used the whole thing in past tense, as if the event already happened, not future tense.

What you wanted to say was "Trump did what the Democrats never could; make it very likely for a Texas Democrat to be elected to the Senate."

By saying "put" you implied the event already came to pass.

English is a dumb language though so understandable for your mistake to be made.

Edit: correction; I missed the first "could" and only saw the second "could". My mistake - the sentence is grammatically correct. Though this is a fine example of why English is a dumb language. Still not as bad as Finnish I'd say (sorry Finns the country and everything is great to me but we gotta fix the language, too many exceptions like English except unlike English you just get misunderstood since so few letters of the alphabet are typically used to make words. Old Finnish had more order than Modern Finnish).