A lot of this malignant polarization was caused by 1) Obama accepting private financing in the 2008 election thereby undermining the McCain-Feingold public financing of elections system. 2) When the Republicans said that they would do everything to obstruct anything Obama tried, the day of the 2009 inauguration, Obama made an incalculably damaging error. He tried to laugh it off - which just stimulated the predatory instincts in the more hateful wings of the Republican Party.
It looks as though Obama never studied social psychology, because if he did he would have realized that at the outset of his term, he needed to go through an assertion of dominance ritual. He should have declared an insurrection, and held an emergency meeting at the Pentagon with these Republican leaders - and had a constitutional proceduralist lecture them on the fact that for a constitutional democracy to work - there needs to be good faith from each branch of government to all other branches of government. He should have had them choose - commit to working for the common interest, of face prosecution for breach of trust to their duties to the general welfare of the country. That was the time he had to stare them down - and get them to understand that deliberate undermining of the Presidency would not be tolerated. He should have learned from the Reagan “laying down the law” in the PATCO case in 1981. Obama was about 20 when that happened - and he should have noted that for the President to not be subjected to taunting and disrespect - it is essential that the President establish limits at the outset.