Senator George Voinovich of Ohio isn’t a cult figure. He has admirers, but no adoring crowds await his pronouncements. He speaks for no one except himself; he’s not one to lead a mass movement or to be a popular symbol.

And yet when the Ohio Republican defected from his party colleagues the other day and balked at swift approval of President Bush’s nomination of John R. Bolton as chief American delegate to the United Nations, he became something of a symbol of the new challenge facing the Republicans who control both chambers of Congress and the White House: how to grow without growing apart.

The Republicans, to be sure, remain in a commanding position in Washington.

They are not about to split apart hopelessly in victory, the way the Democrats do repeatedly in defeat. But more than ever, there are signs that the Republicans are struggling to manage their majority.

It is a natural consequence of political triumph. Two oversimplifications make the case: The Democratic victory in the 1936 election ended up hurting Franklin Roosevelt, not helping him. And the Democratic Party’s successes in the Lyndon Johnson landslide of 1964 were so big that the coalition became unwieldy and eventually led to a fracture that produced the worst possible consequence (two-word summary: Richard Nixon).

The next test of the Republicans’ solidarity comes not on the effort to give Bolton a new position but on the decision about whether Rep. Tom DeLay of Texas gets to keep his current position. DeLay is the House majority leader whose iron hand delights Republicans (most of the time) and infuriates Democrats (all of the time). There hasn’t been such a divisive figure on Capitol Hill since Wayne L. Hays, the Ohio Democrat whose tyrannical rule of the House Administration Committee extended to even the smallest items; in the mid-1970s, lawmakers avoided crossing Hays for fear that he would shut off the air conditioning in their offices. (Hays is now remembered best for putting a mistress, Elizabeth Ray, on his payroll. Ray said she didn’t know how to type.)

DeLay is in a big mess now, in part because he traveled abroad on lobbyists’ dimes, in part because he pays his wife and daughter very well for the political chores they do for him, but mostly because he is not a very pleasant man who has plenty of people who fear him but very few who like him. Neatness may not count, but in politics niceness sometimes does.

The big fight in Washington is over the destiny of DeLay, whom the editorial page of the Wall Street Journal, not exactly a harbor for unreconstructed left-wingers, regards as a captive of the very interests he was sent to Washington to exterminate. He didn’t help himself with remarks last week suggesting that Supreme Court Justice Anthony M. Kennedy was too activist and too isolated. That sort of thing is not done.

This fight has split Republicans at a time when they should be showing enormous unity. And yet they’re battling about other things, too.

They’re still holding post-mortems on the Terri Schiavo case, an exercise that is revealing differences among Republicans in how they view the role of the judiciary in private matters. They are split over whether the Senate should eliminate the use of filibusters for judicial nominations, a particular irony given the artful way conservatives used the filibuster on civil-rights matters only four decades ago.

Republicans are still sticking by their man (the main man, President Bush, if not the hammer-man, Rep. DeLay). They give the president an 87% approval rating, according to a Wall Street Journal/NBC News poll this month. But the same poll showed that removing Terri Schiavo’s feeding tube won the support of 48% of Republicans, with 39% saying it was the wrong thing to do.

Almost three-fifths of Republicans believe that letting workers invest their Social Security contributions in the stock market is a good idea, but, still, 32% of Republicans don’t think it’s a good idea. That may bode ill for the president’s signature domestic priority, especially since the opposition to private accounts is so strong on the Democratic side.

The calendar says the challenges to Republican unity will only mount. The field of GOP presidential hopefuls almost certainly will be the biggest it has been in two decades. In 1988, such major figures as the president’s father, Senator Bob Dole of Kansas, Rep. Jack F. Kemp of New York, and television evangelist Pat Robertson tangled for the nomination. That was a year in which a sitting vice president (George H.W. Bush) was contending for the prize. No such figure appears in the Republican pantheon for 2008, raising the possibility that the party could engage in a divisive free-for-all.

That free-for-all will likely include a Southern social conservative (Senate Majority Leader Bill Frist of Tennessee); an Eastern moderate (Governor George E. Pataki of New York); an idiosyncratic businessman born in Michigan, grounded in Utah and elected in Massachusetts (Governor Mitt Romney); a maverick war hero from the West (Senator John S. McCain of Arizona), a populist war hero from the Midwest (Senator Chuck Hagel of Nebraska); a slow-talking former lobbyist and one-time party chairman from the Delta (Governor Haley Barbour of Mississippi); a Southern son of a football icon (Senator George Allen of Virginia); a true-believing prairie conservative (Senator Sam Brownback of Kansas); and maybe a Pennsylvania conservative who is rising in the GOP leadership (Senator Rick Santorum).

That’s quite a roster. And a roster like that is a recipe for division. The challenge for the Republicans is to assure that it is not a recipe for disaster.