After 18 hours of emotional debate, Vice President Julio Cobos, bleary eyed and visibly nervous, gripped his microphone in Argentina’s Senate building early on July 17 and cast the deciding vote on the president’s attempt to raise taxes on farm exports.

“May history judge me,” he said, as the nation watched on live television. “If I am making a mistake, I ask for forgiveness. My vote is not for, it’s against.”

With that repudiation of his boss, President Cristina Fernández de Kirchner, the mild-mannered Mr. Cobos, a 53-year-old former governor of Mendoza Province, became an instant hero to many Argentines who had grown frustrated with the president’s intransigence during a bitter four-month conflict with this nation’s farmers.

But inside the Pink House, the presidential palace, Mr. Cobos has been persona non grata since casting his vote. The continuing tensions between him and Mrs. Kirchner and her husband, former President Néstor Kirchner, have become a running political soap opera.

“This has been a very difficult situation,” he said last week in an interview in his Senate office, where he has mostly been working in the past four months. “The easiest thing would be to step away from all of this, but I don’t feel I have the right to do that, because the people are saying they want me to stay on and keep doing what I have been doing.”

But Mr. Cobos’s growing popularity has also underscored concerns here that Mrs. Kirchner has run Argentina in a heavy-handed, confrontational way since taking over last December. The president has concentrated decision-making in a handful of people at most. She branded the country’s farmers as coup plotters.

And as the global economic crisis has washed over the world, her government has scared off foreign investors by moving to nationalize private pension funds and the largest airline in an effort to stave off an economic crisis, rather than making bolder but potentially more unpopular decisions.

The independence shown by Mr. Cobos “is a consequence of the intolerant and authoritarian style of the Kirchners,” said Eduardo Buzzi, head of the Argentine Agrarian Foundation, which fought against the president’s farm tax plan.

“Their authoritarianism has transformed their own collaborators into adversaries,” he said.

Since July 27, the vice president has not spoken in person or on the phone with Mrs. Kirchner, said Julio Paz, Mr. Cobos’s spokesman. Cabinet officials have also shunned the vice president. When there have been visits abroad where the president could not go, the Foreign Ministry has sent the provisional Senate president, José Pampuro, rather than turning to Mr. Cobos.

Despite the Kirchners’ attempts to put Mr. Cobos on ice, he has refused to resign — or to stay silent. He has continued to criticize the president’s policies. This month, for instance, he said her decision to nationalize more than $25 billion in private pension funds was premature and would only create more doubts among investors about the stability of Argentina’s investment climate.

The criticism drew a biting response from Mr. Kirchner, whose idea it was for his wife to make Mr. Cobos her running mate. The former president joked publicly that every morning his wife asks him, “What vice president did you stick me with, Néstor?”

In the interview last week, Mr. Cobos called Mr. Kirchner’s comments “unfortunate and misplaced.” He said he had no plans to resign, pointing to opinion polls that suggest that more than 80 percent of Argentines do not want to see him go. “My idea is to continue working in a way that allows me to be true to my convictions and my principles,” he said.

Before the October 2007 election, Mr. Cobos was a little-known one-term governor in Mendoza, where he also served as the minister of environment and public works. A civil engineer by training, he spent most of his career in academia, teaching and serving as a regional dean of the Universidad Tecnológica Nacional.

Mr. Kirchner saw Mr. Cobos, who spent much of his political career with the Radical Party, as a way to broaden the appeal of his wife’s Peronist ticket.

That strategy has backfired. But for now, Mrs. Kirchner is stuck with him.

“For me it would be much easier to resign,” he said. “I could return to being an engineer and live in peace. But I would feel very bad for not having tried, at least, to help prepare this country for the long term.”

Mr. Cobos insists, however, that he has no plans to seek the presidency in three years. “I have a commitment until 2011,” he said, “and then we will see what my destiny is in politics.”

Analysts see those claims as political posturing. Argentina’s opposition remains splintered and rudderless, and Mr. Cobos has as good a chance as any to build himself into a viable alternative, said E. Federico Thomsen, an economist who runs a consulting firm in Buenos Aires. The vice president’s approval rating is twice that of the president in some opinion polls, one reason Mrs. Kirchner has not dared to ask him to resign.

“The incentive is for him to hang on to this very public platform and try to keep his image alive until 2011,” Mr. Thomsen said.

Some opposition politicians are hoping Mr. Cobos can hang on at least until next year’s regional elections in Argentina, when they will try to capitalize on Mrs. Kirchner’s struggles and grab some congressional seats from the Peronists.

Mr. Cobos said his vote against the farm bill ended up helping Mrs. Kirchner more than hurting her. The rejection diffused tensions after months in which farmers had wounded the economy by shutting down highways and limiting exports of grains and soybeans, Argentina’s principal exports. “I am convinced that voting the way I did pacified the country,” he said.

After the marathon senate session, Mr. Cobos, seeking to escape the toxic atmosphere in Buenos Aires, packed up his car and started a 12-hour journey of nearly 700 miles to Mendoza that soon turned into a sort of coming-out party. Thousands of Argentines lined the roads with congratulatory banners and chanted, “You feel it. You feel it: Cobos for president.”

The vice president stopped along the way to talk to supporters and hordes of reporters. The spectacle further enraged the Kirchners, analysts said.

Tensions had simmered somewhat until Nov. 16, when an interview with Mr. Cobos appeared in the Buenos Aires newspaper La Nación in which he criticized some of the president’s policies. A few days later, with Mrs. Kirchner traveling in Africa, he made his first visit to the presidential palace since his fateful vote in July. The newspaper reported that one of his assistants joked, "They took good care of him, but when they brought the lunch one of us tried it first, just in case.”

While criticized for her initial response to the global crisis, in recent days Mrs. Kirchner has announced a series of emergency measures to try to shore up the economy against recession. On Tuesday, she said the government would start a $21 billion public works program and offer tax breaks for investors with money abroad and for companies that recognize unofficial workers.

Mr. Cobos says he remains committed to the basic principles of Mrs. Kirchner’s campaign platform, including the president’s professed efforts to redistribute wealth. But he is pushing against the Kirchners by demanding more federalism and for the provinces to receive a greater share of the revenues they generate, which now flow mostly to the national treasury.

Still, Mr. Cobos said he had no illusions that, as is true of most vice presidents, his power to affect policy was limited.

“Apart from the job of presiding over the senate, the vice presidency is like your health,” he said. “You value it when it is lost.”