In this old commonwealth, the past throws a long shadow and what is familiar tends to muscle aside the promise of change. As Pennsylvania Democrats approach Tuesday's primary, they need to meet the historic moment with the historic courage it demands.

The safe and timid choice would be Sen. Hillary Clinton. Not surprisingly, the former first lady and senator from New York has the support of the familiar forces of the status quo -- party relics and old-style politicians for whom tomorrow is more about today and yesterday, the same old same old.

To be sure, Mrs. Clinton would make her own history if she were nominated and became president as the first woman to reach such heights. And as we observed in Wednesday's editorial endorsing Sen. Barack Obama, Mrs. Clinton is thoughtful, well-versed on the issues and generally qualified to be president.

But Mrs. Clinton is yesterday's woman too, one part of a two-part act with her husband. While the presidency of Bill Clinton may seem a glorious time of peace and prosperity to Americans still suffering the disastrous reign of George W. Bush, the reality was not so rosy. The Clinton years were leadership delivered as soap opera with bitter, partisan division being its stage.

The tens of thousands of young voters who have flocked to the Democrats in recent months were not attracted by the magic of Hillary Clinton. The great mass of defecting Republicans, many of them women, who in their hunger for leadership changed their registrations, did not come for her either.

They came for Barack Obama, a history-making African-American man of all the people. Those who fear him -- not just Republicans but, sadly, other Democrats -- have been furiously trying to come up with a plausible narrative to diminish him. With Lilliputian zeal, they try rope after little rope to tie down the unexpected giant in their midst. This pathetic impulse feeds on the internecine war of the interminable primaries.

Tuesday can put a stop to it. If Mrs. Clinton loses, she loses the last justification for keeping her candidacy alive.

With Mrs. Clinton and Mr. Obama differing little on the issues, Democrats can dare to be different and vote for the truly fresh force in this race, the one who has sparked an excitement and energy not seen since the Kennedy years. The bold choice is Barack Obama, who is uniquely placed to bridge America's most bitter divisions. History now calls on Pennsylvania to lead this nation into the future -- and all it requires is the courage to believe.