On February 13, 2016, Justice Antonin Scalia died. Before his body was in the ground, Senate Majority Leader Mitch McConnell announced he would block anyone President Barack Obama nominated to fill Scalia’s seat. The next week, Jeb Bush dropped out of the Republican primary, quickly followed by Marco Rubio, and eventually Ted Cruz, leaving Donald Trump as the presumptive nominee. Polls showed Hillary Clinton beating Trump by solid margins, with forecasters pegging her chances of victory from 71 to 85 percent, and Democrats favored to take back the Senate.

I was working for Senate Democratic Leader Harry Reid at the time. Being in the minority limited our options for overcoming McConnell’s blockade. But whenever we started to contemplate more aggressive tactics, they were dismissed on the theory that the upcoming election would sort everything out. Why rock the boat, we told ourselves. We’re on a glide path to victory in November, and then President Clinton will submit her Supreme Court nominee to be confirmed by a Democratic Senate.

The rest is history. McConnell’s decision to block Garland consolidated Republican support behind Trump and helped him pull off a narrow victory. Instead of a Democratic president appointing a liberal justice to tilt the balance of the Supreme Court, Trump has appointed two justices to entrench a conservative majority for a generation.

Republicans wielded their power while we hoped for the best. And the course of history was altered forever.

There are two lessons here for House Democrats as they debate whether to open an impeachment inquiry into President Trump.

First, polling can change.

I don’t know how else to say this: getting impeached is bad. It is not something you want to happen to you, especially if you’re president. You do not want to go down as one of only four presidents in history to be impeached. This is a bad thing. Only Democrats, bless our hearts, could convince ourselves that it is good for a president to be impeached.

Richard Nixon’s approval rating was at 65 percent when his impeachment process began and only 19 percent of the public supported his impeachment. By the end, the numbers had flipped: his approval was 24 percent and support for impeachment was 57 percent. Former president Bill Clinton survived because he was popular and the man pursuing him, Independent Counsel Ken Starr, was not. The public rightly thought Starr was on a fishing expedition. By contrast, Special Counsel Robert Mueller is popular and the public thinks he is fair, while Trump is historically unpopular. Even though Clinton survived, his heir apparent lost the next election—which he had been heavily favored to win—while Republicans gained seats in Congress.

The second lesson from the Garland experience is that like nature, power abhors a vacuum. The decision not to impeach is not a decision to focus on other things, it is a decision to cede power, control, and legitimacy to Trump. Trump is not a master chess player, he just bluffs his opponents into forfeiting their moves—and that is exactly what he is doing to House Democrats.

For their part, House Democrats have argued that by foregoing impeachment they can shift the conversation to topics their consultants tell them are safer ground, like health care. That’s not going to happen. Reporters cover news, and only events that drive news can shift the message. House Democrats are understandably proud of having run and won on health care in the 2018 midterms. But their campaign messages were buoyed by a constant flood of major health care news coming out of Washington, DC, driven by the very real threat that Republicans would repeal or replace the Affordable Care Act. But since Democrats took back the House, that’s not going to happen. This is a good thing, but it severely limits Democrats’ ability to drive news on health care. Passing bills in the House that are guaranteed to go nowhere in McConnell’s Senate, as House Democrats recently did with bills to strengthen Obamacare and lower drug prices, will not drive a message.