It is probably true that we all suffer from a bit of "most-important-election-of-our-lifetime" fatigue.

They can’t all be the most important.

Why would this one matter more, say, than 2008, when a president who was supposed to transform our politics was elected?

Here’s a notion: presidents are only as powerful as their first round of midterms.

Franklin Roosevelt promised America a New Deal following his landslide win of 1932, but he began to deliver fundamental change only after Democrats and third-party progressives swept the midterm elections of 1934. That’s when Wall Street realized that they weren’t going to be able to prevent that New Deal. The next year, we got Social Security and the Wagner Act.

Ronald Reagan was going to transform America after his landslide win of 1980, but his Republican Party lost a lot of ground in the midterm elections of 1982. Social welfare programs that Reagan wanted to downsize or eliminate survived in battered but functional form.

Bill Clinton was going to give us national healthcare and end the culture wars after he defeated President George H.W. Bush in 1992. Then came Newt Gingrich’s "Republican Revolution" of 1994 and we got punitive welfare reform and the Defense of Marriage Act, as well as a Telecommunications Act that ushered in a new era of right-wing talk radio.

George W. Bush became president in 2000 only with the help of the Supreme Court his dad helped pick. But in 2002, Republicans swept House and Senate races and there was no stopping the rush to war in Iraq and unprecedented abuses of power at home.

There is every reason to be critical of the compromises and missteps of the Obama presidency. He should have opted for single-payer healthcare and real banking reform. He should have opted against extending the occupation of Afghanistan—for a start.

But elections are not measures of where we have been; they are indications of where we are going. If Democrats lose the House today, as the polls suggest is likely, the first two years of the Obama presidency will be recalled by progressives as the good old days. If Democrats lose the House and Senate, as could happen, they will be recalled as a Golden Age. And if antiwar, anticorporate stalwarts such as Wisconsin Senator Russ Feingold and Arizona Congressman Raul Grijalva are swept out on an anti-Obama wave, there will be a new definition of the word "disappointment."

But this is not about emotions. This is about the cold truth that whatever promise Obama brought with him to Washington in January 2009, will be dashed or realized based on the Congress that arrives in January 2011. That’s not a political appeal, an endorsement or a threat. That’s a practical political reality—based on the historical record of the American presidency.

Obama and his aides might prefer a different measure. But they won’t find one in the history books—at least not in the history books of times such as these.

Midterms matter.

And this midterm matters more—as it will tell us whether the hopes and dreams, the promise and the promises of 2008 were real.

For that reason, above all others, voting is not an option. It is an essential step on the American journey, as what happens today will define the Obama presidency—and the nation—in every bit as meaningful a way as did the midterms elections of 1934, 1982, 1994 and 2002.