There are many theories, most of them political, some of them conspiratorial. But I think it's much simpler than that. Judges.
It's all about the judges.
The democrat party has never been able to sell the country on their agenda which is simply removing any incentive to be productive while in increasing the federal government's power to the point it controls every aspect of our lives. They have made headway over the last century but they had to do it in small increments. At least until the election of Obama. However even then they had to do the majority of it by going around congress. Through executive orders and expanding the powers of various federal agencies. Thankfully the courts rebuffed many of the administrations efforts.
The election of Donald Trump was a shock to everyone. Especially the democrat's base which has become wholly leftist. They need the courts. It's the only way they can win. And President Trump has set them back enormously. He has wiped away decades of court stacking. In his first term he has placed to originalists on the SCOTUS and 44 in the circuits. Another four years of Trump will almost certainly give him two more SCOTUS picks and flip the bedrock of judicial activism, the ninth circuit, conservative.
For this reason Trump has to be removed from office. Now, many scoff and say "that gives us a president Pence". True but what are the chances of an interim president being elected when he is connected to a supposedly corrupt administration? 50/50 at best. If they cannot remove him they need to at the very least keep the Russia hoax alive until November of next year. Hopefully that will convince voters to risk everything on either a Socialist or a closeted Socialist with the door slightly ajar. So far option two seems unlikely. Most Americans didn't care about the Mueller report during the investigation and they equally don't care now it has been released. Anti climactic does not even begin to describe Mueller's findings.
So impeach they must. No one running for the democrats has a chance. They are no different from the base which is completely opposite of everything that made this country great. They loath everyday Americans, see us as Neanderthals who learned to dress. They dismissed us troglodytes in 2016 and paid a hefty price. They are angry. They want their power back. They want revenge.
The key word is power. With power comes coercion and coercion is the only way they can make America Cuba but with newer cars. As bad as the party is we all know they will eventually regain the white house and at some point retake both houses. It's a fact. They will at some point control both congress and the oval office. And, when they do they will hold us down and jam their agenda down our throats. The only thing stopping them will be the courts. Courts two Trump terms will make solidly conservative.
Legislation is no longer the means to enact law. They believe they are morally right and therefore can do whatever it takes to put their policies in place. Eric Swalwell is a great example. He tweeted that as president he would forcibly confiscate "assault weapons" legally obtained by law abiding citizens.. When a conservative commentator replied depriving citizens of their rights would lead to war, Swalwell warned that the government has nuclear weapons.Woud any president unleash nuclear weapons upon America? No, unless it was Hank Johnson. But Swalwell like every other leftist believes the government has the right to force itself on the people. That's not the scary part. The scary part is they are comfortable saying it publicly. That is because they're at a crossroads. Give up or go all-in and they are not about to give up.
Aside from the second Amendment being under siege as it has been for decades the first amendment has come under attack. Years past it was mainly the race card. That shut down free speech and made weak spined republicans collapse like an accordion. However over the course of the Obama presidency the country got tired of it being whipped out every time someone disagreed with the president. Now they have decided they are the arbiters of what is considered hate speech and it's anything that does not jive with their point of view. With the creation of radical groups like Antifa and Black Lives Matter they have decided they have the right to be violent because in their eyes they are morally just. Riots break out on college campuses because conservative speakers are set to appear. There are safe placers for those that feel triggered if they are confronted with the wrong pronoun. Yes, we make fun of them, dismiss them and call them snowflakes but, make no mistake they will eventually be in power and they will push to regulate speech. The Internet, the television, everything. Government agencies will be set up with power, reach and scope that will rival the EPA. Violence will not only continue it will increase and the DoJ will look the other way.
Some time in the not too distant future they will win back power and the only thing that will protect us from them will be the courts. There are no more moderates or liberals or progressives. They are pure leftists. They are seething with hate and thirsty for power. The legislature will become irrelevant under any future democrat administration. If they succeed in removing trump from office they will stack the courts once again with activists and we will be helpless to stop their agenda.
That is why they are obsessed with impeachment.