Democrats are fighting each other after the Hillary loss because the lefties, or progressives, believe the party is not lefty enough.  The lefties believe they lost because Hillary was not "progressive" enough.  They want to take over the party's domestic agenda just as the McGovernites after 1972 took over the foreign policy and national security agenda.

The Hill reported on November 12, 2016:

Progressives believe the Democratic establishment is responsible for inflicting Donald Trump upon the nation, blaming a staid corporate wing of the party for nominating Hillary Clinton and ignoring the Working Class voters that propelled Trump to victory[.]

Lefties do not accept that Hillary lost because she is corrupt and has been investigated by the FBI for the past year, nor do they accept that the Democratic Party has lost the white male vote.  Trump appealed to workers in Pennsylvania, Ohio, Michigan, and Wisconsin who have lost jobs due to NAFTA, free trade, excessive regulation by federal agencies, and high corporate taxes.  Coal miners lost jobs due to the Obama-Hillary war on coal.  Hillary supports partial-birth abortion up to the last minute before birth, which did not attract Catholic and Evangelical voters.  These are all policies favored by the left and Hillary.

The Hill reported that former Colorado Democrat senator Ken Salazar, in charge of the Hillary transition team, said:

Democrats have not done very well in rural America and I don't understand why that has happened. The broader question is how to have a Democratic Party that can attract those working men and women.

Democrats do not understand why they did not do well in rural America and why they did not attract working men and women?  How about not calling them deplorables and bitter people who cling to their guns and religion?

Pew Research reported on November 9, 2016 on the presidential election vote by race and religion.  Trump won the white evangelical vote, the white Catholic vote, and the white men with no college vote by large margins.  The Democrats now wish to further alienate these groups by advocating for late-term abortions, unisex bathrooms, and more free trade.

The Democrats further alienated these white voters by calling them racists who voted for a "white backlash," according to Van Jones at CNN.  This makes no sense, because Hillary is white.  If there were a white backlash, it would have occurred when Obama ran.

Hillary's and the Democrats' push for a 100% domestic "progressive" left agenda is similar to the aftermath of the 1972 election, when the McGovernites took over the Democratic Party's foreign policy and national security agenda.  For example, the Democrats abandoned South Vietnam, allowing North Vietnam to conquer it.  Carter abandoned the Shah, which allowed Khomeini to take over Iran.  Iran then captured our embassy and held Americans hostage, with no adequate response from Carter.  Clinton then failed to respond to the attacks on the World Trade Center (1993), the USS Cole, the two African embassies, the Khobar Towers, and Sudan's offer of Osama Bin Laden himself.

Obama and Hillary continued this weakness by announcing a withdrawal from Afghanistan, which allowed the terrorists to wait us out while killing Americans.  Obama compounded this folly by withdrawing from Iraq without a Status of Forces agreement to leave troops to preserve our victory, thus allowing ISIS to gain control.  This led to more terrorist attacks in our country.  Benghazi and the Iran nuclear surrender are the latest examples.

"Progressives," led by Elizabeth Warren, want to match the McGovernites by taking complete control of the domestic agenda of the Democratic Party.

This is good news for Republicans because they will win more elections.

It is bad for the country because the Democratic Party is totally dominated by leftist ideologues.  It is weak on foreign policy and national security to defend our country, but it favors a powerful nanny state regulating our lives.  It is difficult to see how the Democrats can move farther left.