Especially because this is a headline, it could be an abbreviated use of the figurative term "steamrolled."
On April 25, Politico ran a similar headline: Ryan likely to get rolled on tax reform.
The content of the article begins:
Donald Trump is set to steamroll Paul Ryan on tax reform, the issue the speaker has devoted his political career to achieving. But don’t expect Ryan to relinquish his pet cause easily.
MacMillan offers this definition of steamroll:
To defeat or destroy an opponent completely.
OED also offers a figurative definition and example of "steamroll" in this context:
(b) fig.; (also) to force or drive in a given direction (cf. steam-roller v. 2).
1975 Times 21 July 1/8 The ruling party..will steamroll the endorsement through.
Since the word only appears in the headline, we don't have enough context to know with certainty, but it is not uncommon in headline writing to colloquialize or abbreviate expressions to make a concise point, especially in a piece as informal as the Post article in question. It would be markedly similar to the Politico headline. My interpretation of the headline is that Trump got steamrolled by the Democrats.