That's a rather misleading take. Reagan was threatened with impeachment twice--first by a group of eight representatives over his invasion of Grenada, and later by a lone Representative, Rep. González, over Iran-contra--but it never went anywhere in either instance. González later introduced two resolutions against George H.W. Bush over the Gulf War that were ignored. Those were promptly ignored and died in committee. There was a much larger push to impeach George W. Bush over Iraq and other behaviors, but even there, party leadership ultimately chose to squash the impeachment effort.

When you're talking about such a small number of representatives, it's tough to suggest that "Democrats" did anything as a political party. A few lone voices do not denote a party's position, especially when party leadership was against it.

For that matter, most all of those impeachment efforts at least had a degree of legitimate purpose. One might disagree as to whether actions such as circumventing arms embargoes via illegal arms deals to fund rebel groups prohibited by Congress or (potentially) lying about a foreign nation in order to justify a war are in fact impeachable, but it's difficult to argue that weighing the possibility of impeachment wasn't at least rationally justifiable.