Tuesday, Nov. 4, 2008, is a date that will live in fame (the opposite of infamy) forever. If the election of our first African-American president didn’t stir you, if it didn’t leave you teary-eyed and proud of your country, there’s something wrong with you.

But will the election also mark a turning point in the actual substance of policy? Can Barack Obama really usher in a new era of progressive policies? Yes, he can.

Right now, many commentators are urging Mr. Obama to think small. Some make the case on political grounds: America, they say, is still a conservative country, and voters will punish Democrats if they move to the left. Others say that the financial and economic crisis leaves no room for action on, say, health care reform.

Let’s hope that Mr. Obama has the good sense to ignore this advice.

About the political argument: Anyone who doubts that we’ve had a major political realignment should look at what’s happened to Congress. After the 2004 election, there were many declarations that we’d entered a long-term, perhaps permanent era of Republican dominance. Since then, Democrats have won back-to-back victories, picking up at least 12 Senate seats and more than 50 House seats. They now have bigger majorities in both houses than the G.O.P. ever achieved in its 12-year reign.