Guilt by Association

When someone connects an opponent to a demonized group of people or to a bad person in order to discredit his or her argument.

Despite the tongue-lashing Representative Pelosi and Senator Schumer received, both dug in their heels and flatly denied President Trump's ultimatum.
Donald Trump had zero knowledge or understanding of how our nation's government works, and look at him now! President of the f'n United States!! Heather Nauert knew someone who once worked in the government office, and happens to have been an anchor at the highly respected Fox News Channel before...
President Trump didn't mince words when he said that Obama only did slightly better than him in the primaries.