The last brother is gravely ill, prompting an outpouring of acclaim, even from precincts that seldom have praised him. The Democratic Party is in a swivet over remarks Hillary Rodham Clinton made about the second brother, whose June triumph in the tumultuous year 1968 was undone by his June assassination. A sad spring anniversary – 40 years ago this week – approaches, dreaded by many of the victim’s aging acolytes, their idealism undiminished, their hero’s promise never realized. Who says the Kennedys are in eclipse?

For years, the Bushes have been the American dynasty in the ascendancy. They’ve served three terms as president (about 5 percent of the time the United States has existed), been elected governor four times (of two of the four biggest states, comprising almost one-seventh of the nation’s population), served in the U.S. Senate and the vice presidency, and at the United Nations, the Central Intelligence Agency and in an important diplomatic post in China.

A Kennedy moment

The Bushes may be the family that defines the nation in its third century. Today the Kennedys have almost no political power – but they still retain immense power over all of us. Right now we are again in one of those Kennedy moments.

It began when Sen. Edward M. Kennedy was diagnosed with an inoperable malignant brain tumor. The Massachusetts Democrat is often called the “lion of the Senate,” and his roar has given voice to those without health insurance, without economic prospects, without education or training. He is a liberal – the liberals’ liberal, you might say – but often his hand extended across the aisle, meeting Sen. Orrin Hatch’s to craft legislation on children’s health insurance and hate crimes, meeting George W. Bush’s to shape education law.

In the days since Kennedy’s diagnosis, Republicans and Democrats alike have said that they cannot imagine the Senate without him. The Kennedys have been a prominent part of American history since the senator’s father was appointed the first chairman of the Securities and Exchange Commission, a span that covers about a third of the nation’s history – and that does not account for the political lineage on Kennedy’s mother’s side, which includes John F. Fitzgerald, who more than a century ago became the first American-born Irish-Catholic mayor of Boston.

All three Kennedy brothers – the fourth brother, the oldest, Joe Jr., perished in World War II – served in the Senate and ran for president. Ted’s older brothers inspired two generations of Americans with their intelligence, wit and eloquence. But Ted, perhaps the least quotable but surely the most approachable of the three, is still, at 76, building a formidable legacy.

Few who met the new senator in 1962 (or who watched him in the frantic days after Chappaquiddick) thought he’d become a heavyweight legislator. Nine presidents later, Kennedy is arguably one of the leading dozen senators of American history. His colleagues include Webster, Calhoun and Clay.

Dynasty lives on

Dynastic politics are difficult politics, which is why anything involving the Kennedys and such powerful families as the Bushes or Clintons is fraught with difficulty. Sen. Clinton’s remarks about the assassination of Robert F. Kennedy likely were made in the spirit of saying that presidential nomination fights, like operas, aren’t over until the fat lady sings. But with her opponent, Sen. Barack Obama, provided with early Secret Service protection and with Ted Kennedy facing a serious health challenge, she found herself apologizing for what seemed like a crass reference to Friday’s anniversary of the death of Robert Kennedy.

It was 40 years ago, and somehow that day still seems raw, with the flush of victory erased by the tragedy of an assassin’s bullet. This year’s twin anniversaries of the deaths of Kennedy and of Martin Luther King Jr. fill us with a sense of loss even today – more than that, a sense of unrealized opportunity. What died with both of them was a very powerful sense of possibility. It was sickening and horrible then. Somehow it seems even more sickening and horrible today.

That is because we don’t know what these men might have done. We know only what was done by those who were left behind. (In fairness, we also do not know what errors they would have made, what enduring problems they would have created. But the mind does not work that way. It freezes the dead in their posture of possibility.) So in a few days we will remember, yet again, what happened in 1968 and how much that year shaped America. It created, to start, anger and apprehension, but it created much more than that.

No one living in that year would have guessed the ferociousness of the backlash it created, nor the sheer energy and creativity of the conservatism that it spawned. We are marked equally by them both.

That is the irony of this Kennedy moment. It reminds us, to be sure, of what we have lost. But it also reminds us of how different are our politics and our lives, not just because of what was done to Robert Kennedy, but also because of what Ted Kennedy has done.