A single party dominated Mexico for most of the past century, and its loss 12 years ago proved to many that the country was finally a democracy. Now the nation’s voters seem ready to bring it back to power in Sunday’s presidential election.

The Institutional Revolutionary Party, led by telegenic former Mexico State Governor Enrique Pena Nieto, has held a strong lead throughout the campaign, and also seems poised to retake at least a plurality in the two houses of Congress.

The party has been bolstered by voter fatigue with a sluggish economy and the sharp escalation of a drug war that has killed roughly 50,000 Mexicans over the past six years. The desire for change suddenly works to benefit the party, known as the PRI, which ran Mexico from 1929 to 2000.

It would be a once-unthinkable comeback for the PRI, which many believed was doomed after its 2000 loss and which was still reeling in the last presidential election, when it finished a weak third.

Pena Nieto has cast himself as a pragmatic economic moderate in the tradition of the last three PRI presidents of the 20th century. He has called for greater private investment in the state-controlled oil industry, and has said he will try to reduce violence by attacking crimes that hurt ordinary citizens while deemphasizing the pursuit of drug kingpins.

Mr. Pena Nieto says his party has abandoned the heavy-handed ways of the past and will govern in an open and pluralistic manner; many say the PRI would not be able to re-impose its once near-total control even if it wanted to because of changes in society, the judiciary and Congress.

Lopez Obrador was a centre-leftist as Mexico City Mayor and pioneered some programmes that Mr. Pena Nieto emulated in the neighbouring state of Mexico, such as local pensions for the elderly. But he alienated many voters with his refusal to recognise the narrow victory of National Action’s Felipe Calderon in 2006, declaring himself “legitimate president” and mounting protests that gridlocked much of the capital for weeks.

Vazquez Mota is a former secretary of education and social development in the conservative administrations of President Vicente Fox and his successor, Calderon. She campaigned on the slogan, “different,” but has struggled to distinguish herself from Mr. Calderon while maintaining the support of the party’s power structure.

Also running is Gabriel Quadri de la Torre, the candidate of the New Alliance Party, which has links to the powerful teacher’s union. His poll support remains in the low single digits.

Mexicans are also electing 500 members of the lower house of Congress and 128 senators. Voters will also select Mexico City’s mayor and governors in the states of Chiapas, Guanajuato, Jalisco, Morelos, Tabasco and Yucatan. The president is elected for a single six-year term and cannot stand for re-election.

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