Edward M. Kennedy was romantically described as the last lion, but it might be more accurate to think of him as a river. Especially earlier in his long career, he could be tumultuous and overflow his banks, both politically and in his personal life. But mostly he was steady, forceful, and above all persistent. Particularly in the three decades after his failed 1980 presidential bid, Kennedy didn’t so much charge into political obstacles as patiently wear them down. He pressed on the Senate the way the Colorado River cut into the Grand Canyon.

Kennedy could be a vigorous, unapologetic partisan—as he demonstrated in his landmark 1987 speech condemning Robert Bork, when Ronald Reagan nominated him to the Supreme Court. Kennedy also executed determined rear guard actions against large components of Reagan’s domestic agenda over his two terms, and did not spare the adjectives in denouncing George W. Bush as his presidency grew more partisan and polarizing after its first months.

But mostly Kennedy was a pragmatist, who understood legislation was inescapably the art of the possible. That understanding developed over time: in 1971 Kennedy myopically helped block a universal health care plan from Richard Nixon —one that included a mandate on employers to insure their workers—because he was pushing his own government-run single-payer plan. But especially after his unsuccessful 1980 primary challenge to Jimmy Carter freed him from the burden of balancing his legislative choices against any presidential aspirations, Kennedy became the Senate’s shrewdest assembler of bipartisan coalitions. He came to share, at a bedrock level, the belief that Lyndon Johnson articulated to biographer Doris Kearns Goodwin: “It is the politician’s task to pass legislation, not to sit around saying principled things.”

Actually, Kennedy (with the help of generations of great speechwriters like Robert Shrum) could articulate “principled things” as eloquently as anyone. What Kennedy understood is that there was no contradiction between soaring, uncompromising goals and the inevitably messier work of fashioning imperfect legislative compromises that nudged public policy a few feet down the road toward realizing those goals. Among the reams of outstanding personal reminisces of Kennedy that National Journal has collected today, former Republican Sen. Alan Simpson, a pretty edgy partisan himself at times, captured that quality of Kennedy’s best: “The first obligation of a U.S. senator or congressman is to legislate,” Simpson said. “It means putting an idea into writing and then amending, and then hearings, and then floor management, and conference committees, and warding off vetoes. That’s what Ted did. He was a master legislator.” ...

But Kennedy’s skill at bridging party lines became less relevant in a political world in which legislators faced increasing pressure to stand with their party—and against the other—on all major issues. (That pressure takes the form of everything from nasty blog postings to advertising volleys from party interest groups to full-scale primary challenges.) As Washington has evolved toward a quasi-parliamentary system, the ability of even the most skilled and personable legislators to unite the parties on the biggest issues has diminished. In today’s Congress, the name on the jersey matters less than its color. Kennedy recognized that change and lamented it. When I asked him in 2006 whether other Senators from both parties were now cooler to the kind of bipartisan negotiations he was undertaking with McCain on immigration, he said, “Yeah. The older ones understand it, but it’s not where it is at now.”

That’s not a good thing. Solutions are more durable when the hands that craft them represent a broad range of viewpoints, both inside and outside of Congress. It may be that the ideological distance between the parties—especially with so many Republican moderates having been defeated since 2006—has widened to the point that meaningful bipartisan agreement won’t be possible on President Obama’s big priorities. But there’s no question that the growing pressure for legislators from each party to line up in lockstep formation hampers progress on the big problems that, in Kennedy’s phrase, are “not going away.” There’s no clear path through that intensifying centrifugal pressure—no easy way to forge agreements that could attract broad public support on issues like health care or climate change. But there’s no real alternative either. Obama and Congressional Democrats are not likely to sustain the country’s support without maintaining Kennedy’s commitment to flexibility and the marshalling of diverse alliances—if possible with Republicans in Congress, and if not, then with outside groups representing the full array of interests and perspectives, including those outside of the traditional Democratic coalition....