By Dave Graham
MEXICO CITY (Reuters) - Deep anger over the apparent massacre of 43 trainee teachers has plunged Mexico's Enrique Pena Nieto into his worst crisis as president, but with no credible opposition in sight, mass protests look unlikely to force him from power.
Since the students were abducted by police and handed over to a local drug gang in the southwestern city of Iguala on Sept. 26, a wave of discontent has hit the government, spurring calls at protests and on social media for Pena Nieto to step down.
Pena Nieto has accused unnamed groups of trying to destabilize the government but the public fury is widespread.
Although the protests have been largely peaceful, some demonstrators have clashed with police and even set fire to the door of the ceremonial presidential palace in Mexico City.
Still, the fall of a president would be unprecedented in modern Mexico. And for all the public indignation, no figurehead has emerged to channel the anger and present an alternative.
"You need leaders to start a revolution - and there aren't any," said Mexico City salesman Francisco Aleman, 31, who wants the government out. "The opposition are really divided, so there's no easy way to bring down Pena Nieto."
The leftist Party of the Democratic Revolution, or PRD, has campaigned against human rights abuses in the past but its reputation is in tatters because the Iguala mayor who allegedly ordered the students' abduction was one if its own.
And the horrific events - the government says the drug gang apparently killed all of the students and incinerated their bodies - unfolded in Guerrero state, which the PRD governs.
Mexico's most successful leftist, former PRD leader Andres Manuel Lopez Obrador, has also been sidelined in the uproar because of ties between Morena, the party he formed after leaving the PRD, and the same mayor.
On the right, the National Action Party (PAN), is hamstrung by bitter infighting, allegations that senior lawmakers peddled favors in exchange for illegal payments, and accusations by supporters that it sold out to Pena Nieto in Congress.
In short, the whole political class is in disrepute, said Ernesto Ruffo, an independent-minded PAN Senator.
"The Mexican political system is deteriorating more and more every day," said Ruffo, who became the first state governor in Mexico not to be from Pena Nieto's Institutional Revolutionary Party, or PRI, when he won Baja California in 1989.
Still, Ruffo draws hope from the protests, saying they could force the government to reform institutions and political parties that, as he put it, have become "contaminated by crime".
For years, Mexican leaders have pledged to battle corruption and hold public officials to account. But despite indictments of politicians in the United States, few face trial at home, where the justice system is plagued by incompetence, corruption and the power of criminal gangs.
In Transparency International's 2013 Global Corruption Barometer, Mexicans gave political parties the worst rating of any country polled in the Americas - 91 percent of respondents described them as either corrupt or extremely corrupt.
Much of that is down to the PRI, which had become a byword for corruption by the time it was voted out of office in 2000 after 71 years in power. PRI lawmakers admit there is a problem.
An "urgent signal" needs to be sent to show that impunity will come to an end, says PRI Senator David Penchyna, one of the architects of Pena Nieto's signature reform, a December 2013 law to end Mexico's 75-year-old oil and gas monopoly.
"The Mexican people need to have the hope of believing in their institutions," he added.
So far, the president has done little to disabuse Mexicans of the idea that different rules apply to politicians.
He himself has come under fire for allowing the government to do business with a Mexican company that owned a luxury house in Mexico City that his wife was in the process of buying.
Grupo Higa was part of a Chinese-led consortium that on Nov. 3 won a $3.75 billion contract to build a high-speed rail link in central Mexico. Three days later, the government abruptly canceled it - just before a news report showed that a Grupo Higa subsidiary owned the house of first lady Angelica Rivera.
Under public pressure, Rivera said she would sell her rights to the house. But neither she nor Pena Nieto have addressed the apparent conflict of interest stemming from the government's business with Grupo Higa.
Pressure on Pena Nieto to tackle political corruption is likely to be limited without a stronger opposition.
If he does not act against corruption and police brutality though, further alienation of the electorate is all but certain, said Jorge Buendia, head of polling firm Buendia & Laredo.
"The anger out there is across the board."
(Reporting by Dave Graham; Editing by Kieran Murray)