[A] Isn't there a famous logical fallacy about assuming causality from sequence? [There is: Post hoc ergo propter hoc.] Trump is almost perfect as the polar opposite of Obama, but his election doesn't prove that most Americans rejected Obama, let alone that Obama's faults demanded such a radical change in direction. It seems probable to me that had Obama been able to run for a third term, he would have beat Trump rather handily, but I've come to have a pretty low opinion of the Democrat Trump beat.

I won't try to explain how writers on the right think, but I can give you several thoughts as to why those of us on the left might blame Obama for the rise of Trump:

1. Obama wasted his first two years when he had a Democratic majority in Congress through efforts at bipartisan compromise, including making significant unforced concessions on the budget/stimulus bill (too many tax credits, not enough spending, nothing on infrastructure) and health care. He could have raised taxes to (or above) pre-Bush levels, and as long as the recession lasted return the revenues as stimulus. With oil prices crashing, he could have passed a carbon tax, which would have prodded businesses and consumers to limit oil and coal usage, putting us in sligthly better position on climate change. Both of these would have undercut the debt overhang issue (which was phony and hypocritical, but hurt him politically). ACA is messier, but had Democrats killed the filibuster, they could have passed a better bill (e.g., one with a public option). With more to show, Democrats might have done better in 2010, and the longer Congress stayed Democratic Congress, the more he could have delivered. This is clearer in retrospect, but the one thing I've always faulted Obama for was dismantling Howard Dean's national Democratic Party organization, which produced landslides in 2006 and 2008, and only focusing on his own re-election in 2012.

2. Obama totally bought into the Clinton economic program, with much the same people in charge. He bailed Wall Street out of its mess (and didn't prosecute any of their fraudsters), promoted Silicon Valley tech rackets, undermined unions, and left the less favored parts of the nation -- the same ones hardest hit by the recession -- to fester. He was so locked into the status quo that he reappointed Bush's Fed Chair. He also helped businesses less inclined to help Democrats, especially the fracking boom in oil and gas, and he kept up defense spending. He continued Clinton's efforts at negotiating job-destroying, rent-enhancing trade deals. The net effect was that inequality continued to increase, as it had since Reagan, to unprecedented levels. This engendered frustration and resentment, which left some voters open to Trump's demagogy (especially given that Hillary Clinton only promised more of the same).

3. He promised to change how America thinks about war, then fell right back into the "global war on terror" rut. He kept Bush's Secretary of Defense, and promoted Bush's generals (even the odious and insubordinate Michael Flynn). He escalated the war in Afghanistan, with no success. He pursued drone strikes and targeted assassinations even more aggressively than Bush. His early diplomatic efforts flopped, and were never restarted (although Kerry negotiated deals with Iran and Cuba, which Trump subsequently trashed, as he did the Paris climate pact, DACA, and everything else Obama did by executive order).

4. Obama's whole Democratic Party organization lined up in lockstep behind Hillary Clinton as the 2016 nominee, and she lost, taking Obama's legacy with her. Only Bernie Sanders dared challenge her, and came close enough to suggest that she was out of touch with rank-and-file Democrats, but no one in Obama's elite circle seems to have noticed or cared.

None of these things really explain why Trump won. The roots of that go back to the insane reaction of right-wing media to Obama's win in 2008. Trump was the only candidate who had a personality to match the inchoate outrage whipped up by Fox. He was an outsider, relatively free of the taint of partisan Washington, but was still able to line up the billionaire right-wing donors with their crazy economic ideas. They gambled that they could control the demagugue, much like the far right in Weimar Germany thought they'd domesticate Hitler. Due to his laziness and incompetence, they had more luck this time -- not that Trump didn't leave quite some mess.

The problem with the 60th birthday party is that Obama is still primarily viewed as a political figure -- loved by most Democrats, loathed by most Republicans, in a time of intense polarization so the distinction matters a lot -- and one expects a certain sense of decorum from public servants (exempting Trump). But Obama is not too old to contemplate a post-presidential career, and he's decided to do it in show business. From what little I've bothered to glean from the guest lists -- slighting old political allies (like David Axelrod) in favor of celebrities like Beyoncé and Tom Hanks -- his party was aimed at making a social splash for his new career. Maybe he came off as a bit of an arriviste, but that appears to be the intent, and as far as I know, such events are routine in that set. (Of course, I'd have to revise this if you found a lot of politically active and/or merely rich guests on the list. Like the Clintons, Obama spent much of his political career sucking up to the rich, so he could never quite shake the notion that his end game was to be one of them.)

I don't have an answer to your final question other than to note that Obama's "gravitas" -- his reason, integrity, erudition, empathy, sanity, faith in a very idealized America few of us even recognize except as myth -- didn't play all that well, even among people who voted for him because the Republican alternative was unthinkable. And it certainly didn't convert his sworn enemies, or even make much of an impression on the swing voters. Maybe as a black man he felt he had to be perfect to get elected, but that made him a different kind of target. Joe Biden is a much less imposing figure, and that element of fallibility seems to be working for him. We live in a world where a lot of things are going wrong (pandemic, Afghanistan, climate), so maybe it's better to have someone who cares and reacts than someone who supposedly knows it all and tries to project confidence.

By the way, that last word brings up another peeve about Obama. His economic team convinced him that the key to recovery was confidence -- much like Franklin Roosevelt opened his presidency with "we have nothing to fear but fear itself." It's a truism that economies rise and fall on confidence and panic. But you can't reverse a panic just by pretending confidence, which is what Obama tried to do. (Ron Suskind's 2011 book on Obama's economic team was called Confidence Men. At the time, Paul Krugman regularly made fun of their faith in "the confidence fairy.") But the problem isn't just that confidence preaching doesn't work. More important is that you lose the edge you had to blame your present woes on the people actually responsible for them -- the greedy bankers and the Bush administration that let them run amuck (and, hitting close to home, the Clinton administration's deregulation moves) -- and the people currently trying to prevent the government from helping (Republicans, starting with Mitch McConnell and his "one-term" austerity agenda).