Washington (CNN) On Thursday morning, Ronny Jackson bowed to the inevitable : He withdrew as President Donald Trump's nominee to run the Department of Veterans Affairs.

Jackson continued to deny the allegations against him but said he was stepping aside to avoid being a "distraction" for Trump. Trump, in a phone interview with "Fox & Friends" Thursday, decried the partisan environment and called the way Jackson was treated "a disgrace."

The rise and fall of Jackson is a teaching moment as it relates to Trump, his attempts to change Washington and the lasting effects of political gravity. Here are a few lessons I learned (or re-learned) from the Jackson debacle.

1. The political rules still hold (mostly)

Under past administrations, Jackson might not have been nominated at all (more on that below) and, if he was nominated, would have bowed out within 48 hours of the first allegations of intoxication on an overseas trip and the doling out of prescription sleeping medications. Jackson held on longer than anyone expected but, in the end, political gravity still held. The sheer number of allegations eventually overwhelmed Jackson's ability to respond to them. And the drip-drip-drip nature of how they came out made it impossible for Trump to keep him on -- no matter how badly the President wanted to fight the Democrats and media who he believed were driving the story.

2. Jackson should have never been nominated

Trump picked Jackson because the two had spent significant time together -- White House press secretary Sarah Sanders said no one had spent more time with the President than Jackson -- and he wanted to reward him. He figured that Jackson must have been vetted enough, given that he was the White House physician. And Trump, no doubt, also liked the idea that picking Jackson was out of left field and would surprise all the establishment squares.

The problem with that logic is that it didn't include any sort of serious vetting process, the likes of which most administrations would do as they sought to replace a Cabinet secretary pushed out due to scandal. Sanders said Wednesday that the White House was unaware prior to his nomination of the myriad allegations that came to be made against Jackson. Why not?

Remember that we aren't talking about an isolated incident here. More than 20 people who worked with Jackson came forward with allegations. All of the allegations included in the leaked Senate Democratic memo on Jackson were made by at least two people, according to Jon Tester, the ranking minority member on the Senate Veteran Affairs Committee.

3. Partisanship isn't completely blinding

What did Jackson in wasn't people like Tester. It was Senate Republicans who expressed their concerns with both Jackson's lack of experience managing large organizations and the personal allegations brought against him.

It wasn't Democrats (or the media) who decided to indefinitely postpone Jackson's confirmation hearing, which was initially set for Wednesday. That decision was made by Senate Veterans Affairs Committee chairman Johnny Isakson (R-Ga.) after he received last-minute information that he thought the committee should consider before asking questions of Jackson.

If Senate Republicans had unanimously rejected the allegations against Jackson, you can be sure he would still be the VA nominee. Trump and his White House will push the idea that Jackson was undone by a polarized and out-of-touch Democratic Party. But, what really doomed Jackson was bipartisan skepticism about his readiness for the office to which he was nominated.

4. Where there's smoke, there's (almost always) fire

Jackson, in his statement announcing his withdrawal, insisted that the allegations against him were "completely false and fabricated." Which, um, OK.

It's important to remember that this isn't a he said/she said situation. It's a he said/they said they said they said they said they said they said they said they said they said they said they said they said they said they said they said they said they said they said they said they said situation. (At least; Tester said that more than 20 whistleblowers had come forward against Jackson.)

If these allegations -- or, at least some of them -- aren't true, then why did 20-plus people who had worked with Jackson come forward? Were they all part of some sort of broad smearing effort? If so, how did they coordinate it? And how did they keep that coordination so secret?

Also: Put yourself in Jackson's shoes. Up until two weeks ago, you had an absolutely sterling reputation. Now, not so much. If all of this stuff was just partisan smears, why would you walk away rather than fight? Answer: You wouldn't.

JUST WATCHED Dr. Jackson gives statement on withdrawal Replay More Videos ... MUST WATCH Dr. Jackson gives statement on withdrawal 01:33

5. Being in Trump's Cabinet is like being the drummer for Spinal Tap

Every president makes a few Cabinet picks that don't work out. Or don't work out as well as the president and his top aides had hoped. Very, very few presidents have the controversy and turnover that have hamstrung Trump's Cabinet.

Rex Tillerson (State), Tom Price (Health and Human Services) and David Shulkin (VA) have all been fired or resigned. Jackson and Labor nominee Andy Puzder never even made it to the confirmation stage. EPA Administrator Scott Pruitt may not last the week. And Jeff Sessions (Attorney General), Betsy DeVos (Education), Ben Carson (HUD), Steve Mnuchin (Treasury), Ryan Zinke (Interior) and Wilbur Ross (Commerce) have all been subject to controversy and criticism -- often by Trump himself.

That level of turmoil and turnover is unprecedented in the modern presidency. And it doesn't even include the massive churn in the executive branch among top Trump staffers.

Chaos is the normal now.