I believe some people get upset with what they perceive to be "personal attacks". (Accusing him of not being born in the U.S., proclaiming he is a Muslim, Communist, questioning his GPA at Columbia and Harvard, comparing him to Hitler, one day he's a "dictator" and the next he's weak/ineffective, efforts that are being made in many states to change current voting laws such as reducing he number of days for early, voting, cutting down the number of voting booths in some sections of towns, doing away with Sunday hours for early voting, when there has been no evidence of any significant voter tampering, observing the fact that some people had to stand in line for up to 8 hours to cast a vote.
Some see it as disrespect for the office itself when they saw the Arizona governor sticking her finger in his face, a congressman yelling "liar" at him as he was giving a speech, Glenn Beck poking fun at his daughter when she asked her dad if they had plugged the hole during the BP oil spill in the Gulf, renaming the Affordable Care Act - "Obamacare", slamming his wife and children whenever they go anywhere on vacation..etc
In the eyes of many it's one thing to disagree with the opposition's party philosophy and another thing to attack a person for basically existing. If Obama left office today would president Biden undo the Democrats agenda? Not likely!
The reality is the Democrats were just as harsh on George W. They questioned his I.Q., surmised that VP Dick Cheney and Karl Rove were "really running the country", accused him of stealing the first election, going to war in Iraq to control oil flow and benefit Cheney's friends at Halliburton, being a racist for not responding sooner with aid to New Orleans after Katrina.
The truth is politics has always been a NASTY game! And it's gotten nastier with each election after the George H.W. Bush starting with Ross Perot's "Reform Party" which was a precursor to the "Tea Party".
The last Democrat president, Bill Clinton was eventually impeached after facing every kind of "gate" possible and attacked by likes of Democrat Gary Condit for having an affair while he himself was having one with Chandra Levy.
Hypocrisy runs rampant in D.C. Neither party wants anything good to happen in the country while the other party is in power. If it does that party will use it to justify being re-elected. Party loyalty comes before all else. It's futile to become emotionally invested in politicians.