“For those who had dreamed the dreams of the New Frontier, and shared the hopes of a Great Society, this was perhaps the darkest moment of the entire decade,” wrote Godfrey Hodgson, a British journalist who stands as one of the wisest chroniclers of the 1960s.

Forty years later, is it possible to recapture the hope and energy of the days and years before that April 4? Has liberalism spent enough time in purgatory for the country to revisit how much was accomplished in its name and to acknowledge that the nation is better off for what the liberals did?

In The Liberal Hour, an important new history of the ’60s that will be published in July, Colby College scholars G. Calvin Mackenzie and Robert S. Weisbrot note that for all its deficiencies, the period of liberal sway “demonstrated what democratic politics can produce when public consensus crescendos, when coherent majorities prevail, and when skilled leaders provide direction, inspiration, and relentless energy.”

For decades before the 1960s, conservatism was held in contempt by large swathes of the intellectual and political class. It was one of the great achievements of William F. Buckley Jr., whose death we mourned a few weeks ago, to insist that respect be paid to the great tradition whose cause he championed.

Now is the moment to put an end to our contempt for liberalism. There was business left unfinished on that fateful day in 1968, and it is time to take it up again.