[BRASILIA] Brazilian President Dilma Rousseff launched a last-minute bid Tuesday to block impeachment proceedings against her in what could be her final hours in power.
Her lawyers said they would appeal to the Supreme Court to annul the proceedings before the Senate gathers Wednesday to vote on whether to suspend her from office and launch an impeachment trial.
The result of what is expected to be a marathon voting session may not be final until Thursday.
If she is pushed out, her vice president-turned-enemy, Michel Temer, will take over.
Adding to the instability shaking the Latin American giant, the leaders of the Senate and the lower house spent Monday in open conflict, after interim lower-house speaker Waldir Maranhao tried to order the upper house to halt proceedings - a decision from which he later backed down.
That eased what was looking like an institutional crisis, until state attorneys said Tuesday they would request "the annulment of the impeachment process" by the Supreme Court.
There was no patching over the divisions left in Brazil by the trauma of what Ms Rousseff is daily denouncing as a coup d'etat.
Lawmaker Jose Guimaraes, from Ms Rousseff's leftist Workers' Party, said that despite almost certain defeat in the initial Senate vote, the impeachment trial itself would be an all-out fight.
"We will have 180 days in the Senate, talking with every one of them, to get them to change their minds," he told journalists, warning that "our main fight today will be in the streets."
Police are responding to heightened tension by building a huge metal barricade outside Congress to separate rival groups of protesters during the Senate vote. A separation corridor 80 metres wide and more than a kilometre (half a mile) long will also be enforced.
A square where major government institutions are located will be declared a "national security zone" and made off-limits to the public, Brasilia security authorities announced.
Huge anti-government protests and smaller but still significant pro-Rousseff rallies have been a regular feature in Brazil over the last year, but so far have passed off peacefully.
As Ms Rousseff prepared for her Senate showdown, the man who would replace her continued to work on assembling a new government.
Mr Temer is a veteran centre-right politician but has rock-bottom popularity and would inherit the crumbling economy, now in the deepest recession Brazil has seen for decades.
He has made no public pronouncements in the immediate runup to the Senate vote, but Brazilian media reports suggest he is negotiating with allies on ministerial posts and measures that Congress would pass to try to breathe some life into the economy.
The Senate impeachment trial could last months, running through the Olympics, which open in Rio de Janeiro on August 5 - a first for South America.
Fears over the Zika virus, high crime in Rio, pollution in the sailing and some swimming venues, and a budget crunch are already hurting preparations for the Games, and there are worries that political instability could overshadow the event.
Ms Rousseff is accused of using accounting tricks and unauthorized state loans to boost public spending during her 2014 re-election campaign.
She argues the same accounting techniques were used regularly by previous governments and fall far short of an impeachable offense.
Ms Rousseff, who has vowed not to go quietly, insists that the country's right is using impeachment to topple the left without having to fight an election.
Further complicating the outlook for Brazil is the huge, ongoing corruption scandal centered on state oil company Petrobras.
Dozens of high-ranking politicians and some of the country's richest businessmen have been implicated in the multibillion-dollar bribery and embezzlement scheme, which flourished under Ms Rousseff's predecessor and mentor, Luiz Inacio Lula da Silva.
Ms Rousseff is being probed for alleged obstruction of justice, Mr Lula faces money-laundering charges and some of their fiercest opponents, including the runner-up in the 2014 elections, have also been investigated.
A probe has not been opened against Mr Temer, but a key witness, Senator Delcidio do Amaral, has accused him of taking part in the scheme.
With so much of the political establishment implicated in graft, some are crying foul on the impeachment proceedings.
The head of the Organization of American States, Luis Almagro, condemned the process Tuesday, after meeting with Ms Rousseff last week.
"A high percentage of lawmakers could be implicated, investigated or charged for corruption," he said.
"That definitely creates a structural problem of cynicism regarding the decisions to be taken on impeachment."