Nineteen months ago, Sen. Bill Frist's political ascent ranked among the most impressive in decades. After only eight years in public office, all in the Senate, the handsome heart surgeon was elected majority leader with help from his friend President Bush. Supporters openly speculated that Frist would run for president in 2008.

The Tennessee Republican and his allies have not ruled out a presidential bid, but Frist's rocket ride has slowed dramatically in recent months to an often bumpy, bruising slog. As he absorbs more setbacks than victories this summer, Capitol insiders and analysts suggest Frist's relatively thin legislative experience leaves him poorly equipped to handle one of Washington's toughest jobs. No one is suggesting Frist's colleagues will replace him before his planned retirement at the end of 2006, but the acclaim that greeted his December 2002 rise to the Senate's top post has died down considerably.

Democrats, who control 48 of the Senate's 100 seats, have been nettlesome, for sure. But insiders say that does not explain how a GOP majority -- bolstered by a Republican-controlled House and White House -- suffered a lopsided defeat on same-sex marriage, dropped a class-action lawsuit bill that once seemed certain, failed to reach a budget accord with the House, and failed to pass an energy bill, gun legislation and welfare reauthorization.

In hindsight, these observers say, Frist's backers may have glossed over aspects of his personality and background that tend to undercut his obvious talents.

He has never steeped himself in the Senate's intricate rules and traditions, robbing him of advantages enjoyed by most of his predecessors, including Republicans Trent Lott (Miss.) and Robert J. Dole (Kan.). As a surgeon, Frist is accustomed to having subordinates follow his instructions quickly, and adhering to a workplace hierarchy that is alien to the ego-driven Senate. And while he calls himself patient, Frist tends to shift to a different bill when he hits legislative roadblocks, rather than grind through tough negotiations that probably would involve concessions to political opponents.

Brookings Institution scholar Thomas E. Mann said Republicans should not be too surprised that Frist, 52, is struggling, especially given the Senate's narrow partisan divide.

"Remember, he moved to the leadership suddenly, unexpectedly," Mann said. "He was never the kind of senator who was attracted to the institution itself. He never learned those ways," and sometimes he operates "as though he hasn't quite made his peace with the Senate."

A Mixed Record

Despite an obviously steep learning curve as he settled into his job, Frist helped rack up substantial GOP victories in 2003, including Bush's third major tax cut, the Medicare drug benefit bill, a ban on what critics call partial-birth abortions, and other initiatives that appealed especially to conservatives.

This year has proven more difficult, however, and Frist's defenders increasingly find themselves blaming Democrats' delaying tactics -- which require 60 votes to overcome. Democrats have "taken obstruction to a new low" by filibustering judicial nominees, pressing for votes on amendments that could torpedo legislation and trying to "dictate the terms" of House-Senate conferences, said Senate Majority Whip Mitch McConnell (R-Ky.).

In a recent interview at his Capitol office, Frist expressed similar views in a more reserved manner. "The biggest challenge is addressing big issues . . . in an environment we knew would become increasingly partisan as we got close to the elections . . . with a backdrop of a closely divided Senate," he said.

Academics and some Republicans say Frist's and McConnell's blame-the-Democrats strategy is simplistic and misleading. When one party controls Congress and the White House, they say, it should be able to enact most of its agenda through brute force, patience, compromise or some combination thereof.

Frist is hampered by a divided and "dysfunctional" GOP caucus that will not give him the authority to do what is necessary to pass bills, said Sen. Richard J. Durbin (D-Ill.). "Republicans need ultimately to give Bill Frist the authority to make decisions and move forward."

Frist's relations with Minority Leader Thomas A. Daschle (D-S.D.) -- always civil but not as close as Daschle's dealings with Lott -- were strained by Frist's May 22 visit to South Dakota to campaign for Daschle's GOP challenger, John Thune. Rarely if ever has a Senate leader personally campaigned against his partisan counterpart, and some Democrats were livid.

"It is just bad form working on being bad taste," said Sen. Jon S. Corzine, (N.J.), chairman of the Democratic Senatorial Campaign Committee. "It doesn't feel right historically; it doesn't feel right for the times."

But Daschle turned the other cheek, welcoming Frist to South Dakota and frequently expressing sympathy for Frist's difficulties in running the Senate. In the interview, Frist spoke well of Daschle, calling him a fair negotiator and able lawmaker. "I have tremendous respect for him," Frist said. "He is a good Democratic leader."

Within the GOP caucus, some had expected McConnell, a veteran lawmaker and skilled legislative tactician, to play a bigger role in day-to-day operations on the Senate floor than he has -- similar to the eyes-and-ears role Minority Whip Harry M. Reid (D-Nev.) plays for Daschle.

Sen. Rick Santorum (Pa.), the third-ranking GOP leader, is the most conservative of the three and is a relentless advocate of his causes -- sometimes heeded by Frist, sometimes not. He was the driving force behind the GOP's marathon session on judges last year and this year's losing vote on the same-sex marriage constitutional amendment.

A Fresh, Modern Leader

Republican senators, with Bush's support, essentially drafted Frist into the leadership post after they concluded that Lott had to go because of a racially insensitive remark. A nationally acclaimed heart transplant surgeon with an affable, easygoing personality, Frist was a hero to many Republicans for helping their party regain control of the Senate in 2002, when he chaired the GOP's senatorial campaign committee.

He lacked other leadership experience, but Republicans did not seem to care. They were desperate for a new face after the Lott debacle, and Frist was their ideal -- and unanimous -- choice for leader: smooth and reliably conservative, but without Lott's sharp edges and occasionally loose tongue.

Their confidence seemed well placed at first. While the House endured some wrenchingly partisan battles, especially over the Medicare prescription drug bill, the Senate passed the measure rather easily, 54 to 44. In the process, however, Frist and his GOP colleagues were planting seeds for many of this year's difficulties.

Frist stood by when House Republicans handpicked two Senate Democrats who shared their views to participate in the House-Senate conference committee on the high-profile Medicare legislation, excluding Daschle and other officially appointed Democrats. They barred all Democrats from the conference on energy legislation. On other bills, Frist kept Democrats from forcing votes on their initiatives, such as raising the minimum wage and renewing the expiring curbs on some military-style assault weapons.

Infuriated, Democrats retaliated by refusing to send bills to conference committees unless they were guaranteed participation or major issues were resolved in advance. Democrats also blocked confirmation of Bush's most conservative nominees to federal appeals courts.

A Lost Opportunity

But even when the Democrats' solidarity cracked, the Frist-led Senate sometimes had trouble passing key bills, including the business community's goal of curbing class-action lawsuits. After many setbacks, Frist lined up enough Democratic commitments for a 62-vote, filibuster-proof majority early this year. Between January and June, however, the all-but-certain victory turned into a puzzling defeat.

Frist agreed to a vote on an amendment to raise the minimum wage but balked at other amendments, including a global warming measure and a farm worker proposal co-sponsored by Republicans. Democrats called his decision a deal-killer, and withdrew their support. Frist said he is convinced that Daschle and Reid -- who strongly opposed the class-action bill -- convened their party colleagues "and said, 'No, we're going to kill the bill.' " Not true, says Sen. Christopher J. Dodd (Conn.), one of the 12 Democrats supporting the class-action bill and a key figure in the negotiations. Frist could have dealt with all the amendments in about 20 hours, he said, and even if something objectionable to Republicans got through, the GOP-controlled House probably would have killed it later. "If you really want the [class-action] bill, you jump all over that offer," Dodd said. "They could have done this thing in January."

Sen. Thomas R. Carper (Del.), another Democrat who supported the class-action bill, said the whole episode reminded him of a "TV reality show on a dysfunctional family." Lott said: "I'm still not sure how we managed not to get the class-action [bill] done."

Some senators and lobbyists say Frist appears too unwilling to risk setbacks on measures he opposes in order to clear the path for bigger priorities. For example, one of the amendments pushed on the class-action bill would have required many U.S. companies to reduce their greenhouse gas emissions.

The "climate change" measure's chief sponsor, Sen. John McCain (R-Ariz.), said he did not know whether he had enough votes to pass it, but there was only one way to find out. "Someday we've got to learn that you've got to allow votes on things," McCain recently told reporters. "Otherwise we might as well be the House of Representatives."

Beholden to the Right?

Some advocacy groups complain Frist is too eager to please his party's conservative base. Among the angriest are backers of the U.N. Law of the Sea Convention, a multinational agreement that seemed within reach of Senate ratification last spring after decades of debates and setbacks. Despite the Foreign Relations Committee's unanimous endorsement, Frist kept the measure from reaching a Senate vote after conservative writers -- most notably Phyllis Schlafly -- attacked it and the White House visibly softened its support.

"This is a complete cave-in to the right wing," said Philip E. Clapp, president of the National Environmental Trust.

Perhaps Frist's biggest nod to the right was his recent agreement to allow a vote on a proposed constitutional ban on same-sex marriage, even though it fell far short of the required two-thirds majority. Frist said he was not catering to conservatives but allowing debate on an issue that is bound to gain momentum. "It's an important enough issue that needs to be discussed," he said.

As for the class-action bill, he said, "I'm not going to give up on it. I'm going to bring it back. . . . It's too powerful a bill."

Majority Leader Bill Frist (Tenn.), right, lists Republican accomplishments and discusses legislative goals for the Senate.