ATLANTA (NYTIMES) - Some of the biggest names in American politics jumped into the fiercely contested runoffs for two Georgia Senate seats on Friday (Dec 4), even as a second recount showed that Mr Joe Biden had maintained his lead in the state and Republicans braced for a visit by President Donald Trump, who has railed against his loss there with baseless claims of fraud.

With Mr Trump set to campaign for the two Republican incumbents, David Perdue and Kelly Loeffler, on Saturday, Vice-President Mike Pence and former President Barack Obama held duelling events to underscore the vital stakes in the special elections: If both Republicans are defeated, control of the Senate will shift to Democrats just as Mr Biden moves into the Oval Office.

Mr Obama appeared virtually at a turn-out-the-vote event for Jon Ossoff, the Democrat facing Mr Perdue, and the Rev Raphael Warnock, Ms Loeffler's opponent, and spoke of his frustration in seeing his initiatives blocked by the Republican-controlled Senate when he was in office.

"If the Senate is controlled by Republicans who are interested in obstruction and gridlock, rather than progress and helping people, they can block just about anything," Mr Obama said.

Mr Pence - with Mr Perdue and Ms Loeffler by his side - received a Covid-19 briefing at the Atlanta headquarters of the Centres for Disease Control and Prevention and said later at a rally for the Republican candidates that "we're going to save the Senate, and then we're going to save America".

A second recount of the presidential vote in Georgia has finished, according to the Secretary of State website, showing Mr Biden ahead by about 12,000 votes with 100 per cent of the counties reporting.

New campaign financial reports filed late Thursday showed a staggering influx of money into the state in the first days of runoffs that were expected to set spending records, with more than US$300 million booked in television, radio and digital ads, according to data from AdImpact, an ad-tracking firm. Media buyers said the price of ads was soaring, especially for super PACs, to unseen heights.

The Senate races are playing out at a hyperpartisan moment in American politics that has led to a civil war among Georgia Republicans divided over whether to support Mr Trump as he persists with false assertions that the election was stolen from him. In Georgia and elsewhere, the president's lawyers remain engaged in a failing, last-minute effort to throw the election to Mr Trump.

Even as he tweeted this week that he wanted "a big David and Kelly WIN," Mr Trump called Brian Kemp, the state's Republican governor, "hapless" for failing to work to overturn the election results, while also criticising Georgia's top election official, Secretary of State Brad Raffensperger.

His sustained assault on Georgia's voting system prompted an extraordinary rebuke this week from another high-ranking elections official, who warned of violent threats against poll workers and publicly pleaded with the president to cool down his conspiratorial rhetoric.

On Friday, state Senator Elena Parent, a Democrat on the judiciary subcommittee, which met on Thursday, said that she had been the target of violent, anonymous threats that appeared on a public internet chat room.

The president's appearance in Valdosta, near the Florida border, on Saturday evening comes after a concerted campaign by his advisers and Republican lawmakers to convince him that his presence is vital to increasing turnout among his supporters.

Initially reluctant, the president agreed to hold the rally after being told that victories by the Republican Senate candidates would help prove his contention that his own win in Georgia was stolen from him, according to aides familiar with the conversations.

But some Republicans in Georgia and Washington are fearful that Mr Trump will go off-script and potentially attack Mr Kemp or Mr Raffensperger. Party officials also worry that the president's claims of fraud could backfire, undermining turnout by convincing Republican voters that the special elections are rigged against them anyway.

L. Lin Wood, a lawyer and Republican supporter of Mr Trump, and Sidney Powell, a lawyer who has filed lawsuits on the president's behalf, urged Georgians on Wednesday not to vote "unless your vote is secure."

That same day, a number of prominent Georgia Republicans, including former Gov. Nathan Deal, signed an open letter in which they warned that "the debate surrounding the state's electoral system has made some within our party consider whether voting in the coming runoff election matters."

The leaders said that the party needed to focus on winning the two Senate seats or risk turning the Senate over to a Democratic Party that "wishes to fundamentally alter the fabric of our nation into something unrecognisable."

Some senior Republicans in Washington are doing little to hide their concern about the damage that they believe Wood and Powell are inflicting.

"It's encouraging the president is going down there to rally the troops, because I know there's some inconsistent messages being sent to his base supporters," said Senator John Cornyn of Texas.

Although a hand-recount of the state's 5 million votes reaffirmed that Mr Biden had indeed won the Georgia election, Mr Trump's campaign demanded a second machine recount. Fulton County, which includes much of Atlanta and is the state's most populous, certified its results Friday. As of Friday evening, state election officials had not responded to queries about when they would officially announce the results of the recount or recertify Mr Biden as the winner.

The urgency of the Senate races was reflected in the huge amounts of money pouring into the four campaigns in recent weeks: about US$187 million just in online donations from Oct 15 to Nov 23, according to federal records from the donation-processing sites ActBlue and WinRed.

In that 40-day period, both Democratic challengers outraised their Republican opponents every day from online contributions and surpassed the previous Senate fundraising record for a full quarter. Rev Warnock raised US$63.3 million in online donations, and Mr Ossoff raised US$66.4 million.