Sen. Joe Manchin carries a fateful burden. By quirk of gridlock, he is literally the swing vote between two warring visions for the vote itself. If he gives his decisive 50th vote in the Senate to pass S 1 — the For the People Act — millions are sure to revolt against perceived tyranny from Democrats expanding the franchise with national standards. If he votes no, millions are sure to revolt against perceived tyranny from Republicans restricting the franchise with new state laws. Poisonous division will intensify either way, at least for a time.

Manchin correctly believes that extreme partisanship is a danger signal for American democracy. By the Founders’ design, our “experiment” in republican self-government rests on public trust in votes, which President Lyndon Johnson once called “the most powerful instrument ever devised by man for breaking down injustice.” Yet confidence in republican institutions has frayed for decades by every objective measure, and vote-based American democracy is disparaged or helpless in many countries ruled by autocrats, armies and coups. Wherever democracy weakens, appeals to violence break loose.

The pending crisis is frightful but hardly unprecedented. In fact, hyperpartisanship has been a constant threat when Americans contend over who can vote. Conflict is nearly inevitable because our Constitution does not define the electorate. Nor does it give anyone an explicit right to vote. Voting rights now cherished routinely were once battlegrounds, and U.S. history offers warnings along with lessons for repair.

Manchin’s home state was born from prolonged rancor over voting rules written into the Virginia state constitution of 1776. Virginians who lived in its western counties protested representation that heavily favored property holders and slaveholders east of the Blue Ridge Mountains. The malapportionment was so severe that ex-presidents James Madison and James Monroe, plus the revered Chief Justice John Marshall, supported reform at a special convention in 1829. Delegates were chosen under the current constitutional formula, however, and they rejected “this maggot of innovation.” With only one western representative voting for the status quo result, sectional disputes festered until they split Virginia some 30 years later.

Harpers Ferry changed hands eight times during the Civil War. On April 18, 1861 — six days after the attack on Fort Sumter — wildcat secessionists attacked the same U.S. armory that John Brown recently had occupied in his famously failed attempt to spark an anti-slavery rebellion. U.S. Army troops, having captured Brown for the gallows, burned the armory this time to keep weapons from the expected pro-slavery rebellion in Virginia.

Now the United States teeters at a major crossroads over the vote. So far, Republican senators have rejected every compromise crafted toward bipartisanship. If they remain steadfast in their opposition, and Manchin votes against S 1 for that reason, then Congress effectively will sanction a rash of state laws restricting voters and elections. Similar laws almost certainly will proliferate. They open an ominous backward path for government machinery to control voters rather than vice versa. Aside from violating the core premise of our republic, those efforts cultivate long-term cynicism. Already they have spawned violence on widespread belief that elections are rigged, and partisan denial blocked the bipartisan investigation of a mob assault aimed to overturn our last presidential election.

If Joe Manchin votes yes, S 1 will create what amounts to an affirmative right for every U.S. citizen to vote. (The 14th, 15th and 19th Amendments were phrased negatively to keep excluding voters then deemed unfit.) The lawful mandate of government would facilitate rather than hinder that right, letting candidates and parties compete for constitutional majorities to govern. Voters would gain a fair chance to push both Democrats and Republicans toward higher ground.

Taylor Branch writes books about U.S. history. His “Parting the Waters: America in the King Years, 1954-63” won the Pulitzer Prize.