Progressive Democrats see Sen. Joe Manchin III as a buzzard on a branch, feasting on their agenda as on carrion. Republicans see the West Virginian as the most vulnerable Senate Democrat next year. More disinterested observers consider him an unusually senatorial senator — and someone who could challenge today’s stagnant party duopoly.

Manchin’s deviations from party solidarity began soon after his 2010 arrival in the Senate, when Democratic Leader Harry M. Reid said to him about a particular bill, “We’re all going to be for this,” and Manchin said no, he would not be. In 2020 and 2022, Manchin endorsed the re-election of Maine’s Republican Sen. Susan Collins and Alaska’s Republican Sen. Lisa Murkowski, respectively. His opposition doomed President Biden’s Build Back Better spending blowout. He has forced modifications of some other Biden extravagances — and has been burned by Biden’s reneging on some commitments.

Breaking ranks today, Manchin urges Biden to negotiate concerning the House Republicans’ proposal for lifting the debt ceiling

The Congressional Budget Office projects deficits averaging 6.1 percent of gross domestic product for a decade, up from about 3.5 percent over the previous half-century.

Manchin thinks the nation is “at risk” because of both parties’ commitment to fiscal irresponsibility.

Manchin was 12 years old when West Virginia’s 1960 Democratic primary propelled John F. Kennedy toward the presidency. Manchin has told Biden that he cannot support policies that invert Kennedy’s famous Inaugural Address trope — policies that encourage Americans to ask not what they can do for their country but “how much more can my country do for me.”

Politics is a team sport, but a senator’s principal team should be the Senate itself.

Constitutional equilibrium depends (per James Madison’s Federalist 51) on the three branches “keeping each other in their proper places.” Each should have “a will of its own.” The ethic of party loyalty has destroyed such equilibrium, reducing the president’s party in Congress to a lockstep enabler of presidential agendas. One valuable legacy of Manchin’s Senate years will be his independence in attempting to restore the Senate to its proper place.

The Republican Senate leadership has identified its preferred Manchin opponent, West Virginia’s Gov. Jim Justice, who faces an expensively contested primary. No matter who prevails, for Manchin to win next year he must achieve an extraordinary amount of ticket-splitting, which he did in 2018. That year, after Donald Trump won West Virginia by 42 points in 2016, and before he won it by 39 points in 2020, Manchin won re-election by 3.3 points.

He has long supported efforts to revitalize America’s political center. Today, one vehicle for that is No Labels, the group working to secure, as an insurance policy, ballot access in enough states to make 270 electoral votes achievable for a third candidate heading an improvised party.

Speaking three days after a seismic Washington Post-ABC News poll, Manchin adhered to his previous statement that all options, including a presidential bid, are “on the table.” The poll showed that more than 60 percent of Americans say Biden lacks the acuity to be president.

Manchin is a short-term pessimist but a long-term optimist: Both parties are, he thinks, too risk-averse to address the nation’s rapidly worsening fiscal precariousness, but dramatic improvements can come from policies that are straightforward. For example, quickly do everything to secure the southern border, thereby making possible rational immigration policies that will enlarge the workforce to sustain the entitlement programs.

When Manchin played football he was a quarterback, and he still has an executive’s signal-calling temperament. He will not choose his future path — a re-election campaign, or an even more challenging campaign — until the end of the year.

Then he could, in football parlance, call a consequential audible.