StocksNext year will be a year unlike any other for the stock market. The Republican takeover of the House of Representatives on Tuesday means Wall Street will be contending with three situations in 2011 that drive stock prices: The year before a president faces reelection; the year after a president has lost control of Congress; and the second year of a fragile economic expansion.

The market often behaves a certain way in each of those situations, but investors have never faced this trifecta before. Any mishandling of the economy by politicians, says Robert Doll, chief investment strategist at BlackRock, will mean that “the fragile economic recovery we have is going to be hit over the head, and we would have to think about a double-dip recession all over again.”

The economy is growing at a 2 percent annual rate, according to the latest estimate by Commerce Department officials, slow by historical standards.

Corporate profits are improving, and wealthy consumers are starting to make some costly purchases. If the economy continues to improve, stocks will likely rise. But large gains are unlikely because the economy needs to grow 3 percent or more to bring down the country’s 9.6 percent unemployment rate and residential and commercial construction—the fuel of economic recoveries—remain weak.

So what’s an investor to do given this abnormal year? The best thing may be to follow your long-term plans regardless of what happens in Washington.

“There’s no way to tell what’s going to happen, or we would all be rich,” says Paul Larson, the chief equities strategist at Morningstar.

The Associated Press contributed to this report.