Your recent squabble -- with one questioning whether the other is "qualified to be president" -- highlights how you two have not been giving us the kind of campaign that would best serve not just the Democratic Party but the nation.
The differences between you may be important. But way less important than the need for whichever of you wins the nomination to win in November.
Two extraordinary aspects of our national circumstance oblige you to allow that priority to dictate how you conduct your campaigns.
Let's start with who controls the Supreme Court for the next generation.
If the Republicans win the White House, we would once again get a 5-to-4 majority on the right. In the previous 5-4 conservative-corporatist Court, the Republican appointees helped the strong rather than protected the weak. By gutting the Voting Rights act, they fortified the forces of racial oppression and, with Citizens United, they unleashed big money to further degrade and corrupt our democracy.
Whatever your differences, on the crucial question of the direction of the Court for years to come, you are essentially the same.
That should be reason enough for you to refrain from undercutting each other and sowing division in Democratic ranks.
But there's another huge reason: If the Republicans win the White House, in all likelihood they will control all three branches of government.
Any party having such power, unrestrained by the usual "checks and balances," might be cause for concern. But the idea of such power in the hands of this Republican Party is downright scary.
This is a Party that has blocked measures to deal with every challenge this nation faces--whether climate change, income inequality, or the epidemic of gun deaths. ("If [Obama] was for it, we had to be against it," reported former Republican Senator from Ohio, George Voinovich.) And now the GOP has taken obstructionism to a new level with its unprecedented refusal to consider any nominee, submitted by this duly-elected president, to fill a vacancy on the Supreme Court.
At the state level, the GOP has allowed education systems to be damaged (Louisiana, Kansas) in order to save money that can be used as tax breaks for the rich, and children to be poisoned (Michigan) as a result of measures contemptuous of democracy.
Meanwhile, Donald Trump has become the frontrunner in the Republican presidential race by expressing in more blatant form the bigotry and belligerence and indifference to truth that have increasingly characterized that party.
The battle we need for you to lead is not just against the eventual Republican nominee but against that party as a whole.
Even if one of you is elected president, you will be unable to accomplish anything through the legislative process -- like President Obama these past five years -- unless you take on and take down this Republican Party.
It's time you changed your way of competing against each other into a form that shows you understand what America needs.
Compete with each other over who can best lead this battle, who can best awaken the American people to the threat to our future as a nation this "outlier" Republican Party has become.
Compete over who can best expose the hypocrisy of these Republicans, who make a great show of their love of the Constitution but then twist "advise and consent" into a refusal to consider any nominee because they don't want to lose control of the Court.
Compete over who can best show that the Republican Party has consistently put its quest for power ahead of the good of the nation, and has served the rich at the expense of average Americans.
Compete over which of you can best help the American people see where the responsibility for our dysfunctional politics lies.
Compete in a way that enhances the chances for Democratic victories -- from the White House down to the state legislatures -- by exposing the destructive spirit that has taken hold of the Republican Party.
That job should start not after the conventions but now. Be teammates and competitors at the same time.
This presidential contest is not just about the two of you. It's about the destiny of the nation, about whether our political system can be made able to work for the nation's good again.
You have declared you want to be our leader. Lead now. Start now to unify and mobilize our forces, and lead us into battle against a once-respectable political party that's gone off the rails.
Andrew Bard Schmookler is the author of What We're Up Against: The Destructive Force at Work in Our World--and How We Can Defeat It.