Dems know they do not have anything resembling a solid case to impeach Trump. But they want to keep The Narrative alive so that when the pendulum shifts as it always does and they eventually return to the White House, they can make the argument that:
Trump something something something so his Supreme Court nominees are illegitimate and something something something lower court appointees are something something something and his Executive orders don't count because something something something and every piece of Congressional legislation signed into law are Unconstitutional because something something something. So now the Democrats should be able to come in and pretend the Trump Presidency never happened.
And if you disagree, then you're a racist