Mexican President Enrique Peña Nieto may be forced to rely less heavily on Congress, as preliminary results for Sunday's mid-term polls give his Institutional Republican Party (PRI) a mere simple majority in the Chamber of Deputies, in an election marred by violent protests.
Estimates from the National Institute for Elections (INE) give the PRI 196 to 203 of the 500 seats in the lower house, ahead of their main opponents of the Party for National Action (PAN), who are set to receive between 105 and 116 seats.
These estimates do not yet guarantee that the government coalition, regrouping the PRI, the Green Party and the small New Alliance party, will retain their current slim majority of 251 seats combined.
All 500 seats of the Chamber of Deputies, the lower house of the Mexican Congress, were up for grabs, as well as 9 out of 31 governor posts and thousands of municipal and state offices, Reuters reports.
But the ruling coalition is also expected to be challenged on a state and local level.
According to the Mexican daily Milenio, at least five out of the nine incumbent governors will not be re-elected, and in the northern state of Nuevo Leon, an independent candidate looks assured to become governor for the first time in the country's history.
The election was expected to be the largest in the history of the country, with more than 87 million citizens being entitled to vote, according to the leading daily La Jornada.
But the INE estimates actual participation at less than 46%.
While the previous mid-term election in 2009 also saw similar abstention rates, one additional explanation for many voters staying at home this time might be the violent build-up to the election.
Protests over disappeared students
Several federal states saw widespread violence and protests ahead of Sunday's vote, particularly the southern states of Oaxaca, Michoacán, Chiapas and Guerrero, AP reports.
The protesters were largely directed towards the state's handling of the disappearance of 43 students from Tixtla, Guerrero, in September 2014.
The students, from the notoriously activist teachers' college of Ayotzinapa, were arrested by local police in the wake of a political protest and are thought to have been subsequently handed over to a local drug cartel and executed, according to AFP.
Only one of the students has been confirmed dead by forensic tests, but the families of the remaining victims refuse to believe that they are dead.
They have been conducting large-scale protests since September, and many Mexicans across the country have joined the protests in solidarity, showing concern over the covert collaboration of cartels and local officials, as exemplified by the disappearance of these students.
The relatives of the disappeared stole and burned election material ahead of Sunday's polling in Tixtla, preventing several polling stations from opening on Sunday.
La Jornada further reports that major clashes between police and sympathisers with the relatives' movement occurred in the neighbouring state of Michoacán.
Teachers take over polling stations
Another source of violent confrontations has come from the teacher's syndicate, the CNTE. The union is protesting a major education reform initiated by President Peña Nieto to improve the country's school system, particularly its plans to evaluate teachers based on performance, Reuters reports.
The union held protests in various areas of the country, burning thousands of ballots and ransacking headquarters of political parties, according to AFP.
The protests have been most intense in the city of Oaxaca, where the radical "Section 22" of the union is based.
The secretary general of Section 22, Rubén Núñez, assured Milenio that the organisation's 81,000 members were ready to sabotage Sunday's election.
"We will show [the government] that we will be watchful of this process and ensure it is not carried out," he said.
Section 22 kept their word, and on Sunday occupied 11 of Oaxaca's polling stations ahead of the election.
Despite a massive police and army intervention, the teachers remained in control of three polling stations and had devastated the ones they gave up, La Jornada reported. This prompted several local election officials to call for the election to be postponed, justifying this demand by the fact that "the process has been militarised, aside from the recovered facilities being inoperable".
Intimidation from drug cartels
These protests come in addition to intimidation campaigns by drug cartels that have so far claimed the lives of at least seven candidates and nine campaign officials, according to Reuters. Mexico has a long-standing problem with such cartels, which pose a significant challenge to federal rule in many regions.
The federal government has responded with a massive deployment of security forces.
Up to 25,000 police officers monitored the election in Mexico City alone, La Jornada reports.
An additional 40,000 military and police personnel were sent to secure the troubled southern states, according to Reuters.
Mexican Secretary of the Interior Miguel Ángel Osorio Chong in a press release stressed the importance of "guaranteeing the conditions that will allow citizens to exercise their right to vote in a free and peaceful manner" all over the country.
The definitive election results will be available Wednesday at the earliest, according to the INE website.