Whether or not Republicans regret that Sen. Arlen Specter quit the party, his departure underscored an undeniable problem for the GOP: It's shrinking.

In Pennsylvania, more than 200,000 registered Republicans switched to the Democratic Party last year, giving Democrats an edge of 1.2 million.

Nationally, only 21 percent of those polled identify themselves as Republicans, the lowest level since 1983. Thirty-five percent called themselves Democrats, and 38 percent independents.

Government works best when there are checks and balances. We saw how it works worst when former President George W. Bush ran amok with a Congress controlled by his own party.

With Specter becoming the probable 60th vote for Democrats, Republicans lost their ability to provide a check on Democrats. If the GOP is to have any effective input in shaping policy in Washington, it needs to expand its appeal.

The GOP too often has laid down rigid conservative markers on issues such as abortion, gay marriage and immigration. Those stances alienate moderate voters who otherwise would be drawn to the party's traditional platform of lower taxes, limited government, and strong national defense.

Democrats have made gains in part because they haven't shunned all of those who disagree with liberals. For example, Sen. Bob Casey of Pennsylvania is pro-life and opposes gun control, and he's a rising star in the party.

The man getting much of the blame for the Republicans' plight is Pat Toomey, the conservative whose candidacy drove Specter from the GOP. Toomey said Republicans are out of office "because they let people down."

"Elected Republicans need to demonstrate they are committed to the principles they advocate," Toomey said. "The core idea is limiting the power of government. It's the fundamental opposite of the Democrats."

The GOP became identified with big-government spending and intolerance on social issues, losing support in droves. To remain competitive, the party needs to make room for people with whom conservatives sometimes disagree.

The large swath of voters who call themselves independents are an opportunity for the GOP. Independents should also serve as a caution to Democrats not to let success go to their heads.

There are still strong points for the GOP. It is firmly in control of the state Senate in Harrisburg, Pa. In New Jersey, Republican candidate Chris Christie is leading Gov. Jon Corzine in polls.

And it wasn't that long ago that the Democrats were floundering and out of power. Times change and events often influence public opinion. But if the GOP wants to remain competitive, it needs to reach more Americans in the broad center.