Washington ? Politicians fear nothing more than what they call an “October surprise” Â a mid-autumn jolt that shapes voters’ decisions at the polls. Ordinarily this fear is centered in foreign affairs, where a pre-election diplomatic initiative or military engagement can shift the political balance of power. This year’s fear is the October surprise that will accompany the arrival of the third-quarter 401(k) statements.

Those reports, which will arrive in voters’ mailboxes a month before the midterm congressional elections, are the principal reason why the Senate, which ordinarily lopes, meanders and wanders, this week created a stampede. That stampede approved major adjustments in accounting regulations, but also was a way to assure the American people that the companies they invest in operate in sound ways  and a way to assure their own survival at the polls in November.

The closing bell rings in the markets every weekday, but the only political bottom line that matters is Nov. 5, when voters stung by plummeting share prices will determine control of Capitol Hill.

That’s why the Senate chamber echoed with calls for “fundamental fairness and efficiency in our economy” from Democrats such as Sen. Joseph R. Biden Jr. of Delaware and with criticism of “egregiously bad behavior of corporate insiders” from Republicans like Sen. Charles E. Grassley of Iowa.

But beneath the rhetoric on Capitol Hill this week  and the torrid days that preceded the vote  are two subliminal calculations that every politician fears but none speaks. The first is that in a year in which the word “security” is freighted with special meaning, no political figure can ignore any assault on American security, whether it is personal security, military security or financial security. The second is that precisely 20 years ago a Democratic Party frustrated by the charm and popularity of a Republican president made substantial gains in midterm elections by stressing Americans’ retirement security.

These two notions form the double-helix that controls political behavior in Washington this summer. And, 10 months after the terrorist attacks of September, behavior in Washington is once again plainly, decidedly and relentlessly political.

The financial markets have been an especially important factor in American politics in recent years. A set of statistics explains why: In two decades’ time, the portion of Americans’ wealth that was tucked away in traditional bank deposits has fallen by half; by December 2000, the Federal Reserve was estimating that half of American households owned shares in at least one mutual fund. And the Employee Benefit Research Institute estimates that the average 401(k) account held $49,024 at the end of 2000, the most recent year for which figures are available.

Employee contributions and employers’ matches in investors’ 401(k) statements might blunt the shock in the next retirement savings statements to arrive in Americans’ mailboxes, but politicians are showing that they are taking no chances.

Republicans were at pains, for example, to show that many of the accounting scandals that have become the wallpaper of the summer news actually began during the administration of Bill Clinton. But in the Clinton years almost everybody in the financial markets made money. Now that’s over  and behavior that was ignored, by regulators and reporters, in a bull market is casting a long shadow in a bear market.

Democrats know, moreover, that their most stunning success in midterm elections in the past generation occurred in the first congressional contests after the inauguration of Ronald Reagan, when they gained 26 House seats by transforming the election into a contest over retirement security. The decision by Speaker Thomas P. O’Neill Jr. of Massachusetts to make the survival of Social Security the main theme of the 1982 election is a chilly shadow for Republicans.

Lawmakers of both parties spoke easily in the past several months of how the terrorist attacks created a fundamentally different world on Capitol Hill. They were speaking mainly of a new consensus on increased spending on military affairs and homeland defense. Only in the past several weeks have they recognized that the world is fundamentally different in economic affairs as well. The best measure of that isn’t the end of the surplus; lawmakers knew months ago that new spending would cause a new deficit. The best measure is one of the most popular elements of the tax bill Congress passed only last year; it enhanced college-savings plans known as 529 accounts, which permit Americans to shield from taxes market gains on college-savings plans.

The assumption that market prices would continue to rise, and thus require tax protection, is gone now. America’s investors and the nation’s politicians are in the same fix. They both are worried  and, sharing a lack of confidence and a new surfeit of peril, they have cause for more worry.