With President Trump's approval rating consistently maxing out around 42 percent, it can seem that there is just one way for Republicans to retain control of the White House in 2020: They must thoroughly demonize the Democrats — relentlessly labeling them America-hating, baby-killing, economy-wrecking, Israel-loathing, freedom-shredding socialists. Add six or seven percentage points of Demophobic "swing" voters to Trump's solid base of support and he will prevail, even if a solid majority of Americans consider the president personally loathsome.

But there is another way Trump could win: if the Democratic Party splits. The chance of that happening is probably greater in this election cycle than in any since George McGovern's faction of anti-war progressives seized control of the party in 1972, leaving Cold War liberals out of power for the first time since the Truman administration.

This time around, tensions in the party may be greater — and the risk of outright fracture even higher — than they were nearly half a century ago. Yes, today's Democrats are united in their hatred of the president. But that is where party unity ends.

Spend time on Twitter following Democratic activists and pundits and you'll be tempted to conclude that the party is divided between different factions of left-wing progressives. Some are enthusiasts of Vermont Sen. Bernie Sanders, who unwaveringly believe the self-described socialist is the only option for 2020. Others, meanwhile, pine for a woman or person of color to be the party's standard-bearer and will settle for nothing less. Many of these Democrats are flocking to Massachusetts Sen. Elizabeth Warren, while others gravitate to California Sen. Kamala Harris.

Even if this were the only serious divide in the party, it would present a potentially ominous challenge, since many of those committed to Warren and Harris harbor lingering anger toward Sanders and his online brigades of toxic "Bernie-bro" enthusiasts and obsessives, whom they partially blame for Hillary Clinton's defeat in 2016. Whether these anti-Sanders Democrats would come around to supporting the supposed ring-leader of these misogynist bullies is anyone's guess. But at the moment, it looks unlikely.

However, polls reveal a party riven by a different and deeper divide — one separating the ideological left in all of its squabbling factions from the ideological center. Sanders is the clear leader of the former camp, and former Vice President Joe Biden (whose entry into the race is supposedly just days away) leads the latter. Most of the recent polls show Sanders and Biden polling somewhere in the 20s; some have Biden in the lead while others give that honor to Sanders. What's clear is that the two factions appear to be pretty evenly matched — something one would never glean from online discussion and debate, because Biden supporters are quite thin on the digital ground.

This split among Democratic voters at large, if it persists through multiple debates and nine months of campaigning, could well portend a primary season that ends indecisively — without the party reaching consensus on which faction should be the one to take on Trump. That could culminate in a real mess at the Democratic National Convention in Milwaukee.

Let's assume Biden prevails — either by winning enough delegates outright heading into the convention or by losing on the first ballot at the convention but then coming out on top during a subsequent ballot (when the party's superdelegates are allowed to weigh in). Will voters who favored Sanders accept that outcome and support the former vice president? And will those who preferred Warren or Harris and were unsure about whether they could motivate themselves to work up enthusiasm for Sanders, an old white man who is at least impressively progressive on most issues, get themselves to rally around Biden, an old white man who stands for everything they want the Democratic Party to leave behind?

I'd say it's far more likely that a significant number of these committed leftists will bolt the party in disgust, looking to throw their weight behind some other, purer alternative in the general election. That would be politically foolish in the short term, ensuring a victory for Republicans. But for those who despise the milquetoast Democratic establishment, it would also be a highly satisfying way to demonstrate that establishment's impotence to the world — by working to ensure that it fails in its effort to defeat a widely despised president.

That's one way the Democrats could fracture. Another would involve Sanders prevailing outright or on a later ballot at the convention. It's possible that the party's Clintonian elite would consider this an act of political malfeasance and worry about its fundraising implications. But it's unlikely Biden or any other prominent centrist Democrat would set out on a kamikaze mission to sink the Sanders campaign as it strives to take down Trump.

Whether Biden or Sanders prevails in the primaries, possible peril awaits, which is a powerful case for finding some other option — a consensus candidate who can bridge the ideological fissure that runs down the middle of the party. Hence the appeal — at least in the abstract — of Harris, or Beto O'Rourke, or Pete Buttigieg. All three candidates have a knack for speaking in airy platitudes aimed at the median member of the party and carefully crafted to avoid antagonizing any faction in particular. Each wants to be all things to every Democrat.

Can it work? At the moment, Buttigieg seems to be the one on the verge of breaking away from the distant second tier of candidates to compete in the polls with frontrunners Biden and Sanders. But can he — or one of the other consensus options — catch and surpass them? The outcome of the 2020 election, no less than the future of the Democratic Party, may hang in the balance.