Venezuela rings in its official presidential election campaign this Sunday. President Hugo Chávez and Henrique Capriles, the candidate of the united opposition, have both registered as candidates. The coming months could prove to be Chávez’s toughest yet. They could also put the country on edge as uncertainties over his health lay bare its fragility and ill-preparedness for a potential transition.

Under normal circumstances, Chávez would not have much to fear. He still enjoys the support of many Venezuelans who perceive that their lives have improved under his Bolivarian revolution. With strong emotional ties to his core constituency, the president has successfully distanced himself from governance problems — such as exorbitant crime rates — even as popular support for his administration weakens. He also commands loyal institutions, controls the state media and openly uses the public purse for his campaign.

But these polls are different. Like Chávez, Capriles has never lost an election. For once, the opposition has united behind him. Although most polls still give the president a two-digit lead, the number of still undecided voters is relatively high — Capriles’s moderation might well resonate with them. More important, however, the president must compete against not only Capriles, but also cancer. The severity of his illness remains unknown, and the lack of reliable information has fueled uncertainty and speculation.

For good reason. With no clear succession mechanism or obvious heir to Chávez, his ruling party is nervous: Chavismo would be in trouble without Chávez. Many around the president have much to lose, starting with senior government and military officials facing allegations of drug-trafficking.

Beyond Chávez’s inner circle, the country as a whole seems ill-prepared for transition. Society and politics are polarized and institutional conflict mechanisms eroded. Add to this the large number of weapons circulating, burgeoning criminal violence and openly politicized armed groups operating outside of state control, and the spectre of a potentially violent political crisis becomes sharper.

A crisis could play out in several ways. The ruling party might seek to suppress unfavorable electoral results or, if the president’s health declines abruptly, delay the vote to buy time to determine a replacement. Either scenario could spark opposition protests, perhaps even leading to open confrontation.

Several factors may temper risks, however.

• First, Chávez himself has always rooted his legitimacy in the ballot box and promises to accept October’s results. Although far from fair, Venezuelan elections are not easy to steal wholesale. The electoral authority, the Consejo Nacional Electoral, may be less prone to government interference than others.

• Second, any blatant violation of the constitution would probably hinge on the support of the armed forces, which even the ruling party cannot bank on. The top brass may be loyal to the president, but generals and the ruling party could not necessarily count on the unconditional backing of the middle and lower ranks, many of whom are reportedly upset about the institution’s politization under Chávez, Cuban influence and the creation of competing militias.

• Third, important neighbors such as Colombia and particularly Brazil are unlikely to go along with unconstitutional acts. Even the Castro brothers, highly dependent on oil and ideologically aligned with Chávez, might be pragmatic enough to see that the island’s interests are not best served by binding it to an illegitimate and probably isolated regime with an uncertain future.

Nevertheless, Chávez’s illness and the issues at stake take Venezuela onto unknown and unpredictable terrain. Venezuelan leaders should publicly and forcefully renounce the use of violence and pledge to respect the constitution. The Electoral Council should not risk its reputation within Venezuela or beyond by succumbing to executive meddling. It should enforce the campaign rules, invite international observers and stick to its electoral calendar — and the final results.

Finally, the public disclosure of Chávez’s prognosis — as has happened in similar situations elsewhere on the continent — could be the medicine Venezuela needs. It would lessen voters’ uncertainty about whether their president is physically capable of running the country, while allowing the ruling party to either unite behind him or take measures to prepare a replacement.

For President Chávez himself, how he handles his illness and the months ahead will do much to shape his legacy.

Silke Pfeiffer is the Colombia/Andes project director of the International Crisis Group. She is based in Bogotá.