Donald Trump wasn't welcomed warmly at the World Series on Sunday ... some fans hung "Impeach Trump!" banners in the stands while others booed the president relentlessly.
POTUS made his first appearance at the Astros-Nationals series in Game 5 at Nationals Park in D.C. ... and he was almost immediately hit with negativity.
When 45 was shown on the jumbotron, cameras caught fans booing him loudly ... with a "Lock him up!" chant breaking out in parts of the stadium.
Later in the evening, several people -- including some in Nationals hats -- unfurled multiple "Impeach Trump!