By noon last Tuesday, Senate Majority Leader Bill Frist seemed done with John R. Bolton's nomination to be U.N. ambassador. Bustling from the Capitol to have lunch with President Bush, he told reporters he planned no further votes to try to end the Democrats' long-running filibuster of the embattled nominee.

But after his presidential chat, Frist announced he would keep trying, prompting newspaper headlines such as "Frist Reverses Himself," which his staff called unfair.

The next day, the Tennessee surgeon-turned-politician again seemed to wash his hands of Bolton. "It's really between the White House and Chris Dodd and Joe Biden," he said, naming two senior Democratic senators. At 11 p.m., however, he was working the phones, successfully urging another conversation between Biden and White House Chief of Staff Andrew H. Card Jr. But the late-night Biden-Card call did not resolve a dispute over documents at the heart of the Bolton impasse, and Frist had little to show for his work but negative news reports and political headaches.

"It's not easy being Senate majority leader," Robert J. Dole said in an interview Friday. The Kansas Republican knows it well. Like Frist, Dole learned the post is even harder when its occupant is running, or even thinking about running, for president. He resolved the conflict by resigning from the Senate in June 1996, though it did not save his campaign against President Bill Clinton.

Dole, 81, is sympathetic to Frist's plight. "I think he's done a good job," he said, adding that Frist would be a strong presidential contender. But others, noting Frist's uncertain handling of the Bolton nomination -- plus last month's bipartisan deal on judicial nominees that left him on the sidelines -- wonder whether he is up to the task.

"I think he's very bright, but he had never been in hardball politics," said former senator Alan Simpson (R-Wyo.), referring to Frist's comparatively swift and painless ascension to the leadership post in early 2003. "Politics is a contact sport."

Simpson, who heartily praises Frist, said the majority leader is learning Dole's lesson about the perils of dual ambitions, even though the 2008 presidential race seems far away. "The minute Frist or others felt he was running for president, then there was a diminished opportunity for getting things done," Simpson said from his office in Cody, Wyo.

Some nonpartisan analysts see deeper shortcomings in the way Frist approaches difficult issues, such as judicial nominees and Bolton. He sometimes compounds his problems, they say, with ill-timed comments and actions that a cannier Senate leader might have avoided. "We still see a bumpy learning curve," said Norman J. Ornstein, a congressional scholar at the American Enterprise Institute.

For example, he said, Frist could have sidestepped Tuesday's row over Bolton simply by deferring comments until after the White House lunch, at which he knew Bush would discuss the nomination.

On broader and more complex issues, Frist's tendency to stake out early and firm positions has restricted his ability to negotiate in the crucial later stages of compromise efforts, when leaders sometimes need every inch of political leeway. As early as Nov. 11, he made a speech suggesting Senate rules should be changed to ban filibusters of judicial nominees. When the matter finally culminated more than six months later, the bipartisan "Gang of 14" drafted their accord in a room that excluded Frist, as well as Democratic leaders.

"He showed his greenness in a way that took away his running room," Ornstein said. "Going and meeting with some of these groups, that left him no way out."

Part of Frist's trouble is that he is courting two very different audiences at once, said Michael J. Sandel, a Harvard University political scientist. With staunch conservatives playing big roles in GOP primaries, and Senate centrists often crucial to resolving contested legislation, he said, "the constituencies are in tension with each other."

Frist has appealed to conservative activists through his decisions on judicial filibusters and the Terri Schiavo case. He drew widespread ridicule in editorial cartoons for his long-distance questioning of whether Schiavo was really in a "persistent vegetative state" after viewing her on a videotape. "His leadership of the Senate has faltered so far as he has tried to cultivate the constituency of Republican primary voters," Sandel said.

Frist's aides dismiss the criticism. "This is a guy who is consistently underestimated," said his spokesman, Bob Stevenson. He points to several previously stalled bills that have passed this year, including those restricting bankruptcy protection and class-action lawsuits. He also credits Frist for bringing long-fought comprehensive bills on energy and highway construction close to completion.

Frist's chief of staff, Eric M. Ueland, says the senator's team "rewrote the president's tax policy to move the tax cuts up earlier -- a decision that Frist made -- so we'd get more bang for the buck." He called the landmark legislation adding a prescription drug benefit to Medicare "the Bill Frist prescription drug bill."

But when it comes to Bush's bid to restructure Social Security -- which is languishing in the Senate Finance Committee while Frist has been largely quiet -- Ueland and Stevenson emphasized another facet of Frist's leadership strategy. He is "restoring and enhancing the power of the committee chairmen to work the process through in each committee before they bring legislation to the floor," Ueland said.

Ueland said Frist is so reluctant to trumpet his endeavors -- such as brokering phone calls at 11 p.m. -- that many in the news media and public sell him short. "This is a very different kind of politician," he said.

Senate Majority Leader Bill Frist (R-Tenn.) has been criticized for his handling of judicial nominees and the John R. Bolton nomination.