US President Donald Trump was increasingly isolated on Friday, with top Republicans and conservative media allies rejecting his claims of widespread voter fraud as his chances of election success almost evaporated. Mr Trump posted an erratic series of Twitter messages from the White House as his Democratic challenger Joe Biden, 77, made gains in key battleground states and readied to deliver a prime time national television address. The 74-year-old president continued alleging widespread voter fraud and counting irregularities in Tuesday’s election, but some key Republicans rejected the unfounded claims as Democrats readied to welcome Mr Biden as president-elect. With his presidency hanging by a thread, Mr Trump said it was vital to have a Republican in the West Wing to keep a check on a Senate in which left-leaning Democrats gained seats in the November 3 election. “With the attack by the Radical Left Dems on the Republican Senate, the Presidency becomes even more important!” Mr Trump told his 88.4 million followers on Twitter after it became clear that Mr Biden was on track to win the presidency. Mr Trump posted a series of missives after Mr Biden took the lead in Pennsylvania, where a haul of 20 electoral votes would put him past the 270 threshold for victory in Tuesday’s vote. The former Vice President also made gains in Georgia. Mr Trump also quoted the conservative lawyer Ken Starr, who said Pennsylvania had “conducted itself in a horrible lawless way” and “flagrantly violated the constitution” by excluding observers from poll-counting centres. “We have to go back to the state level and how this morass came to be in the first instance,” added the president, in reference to the adjudication powers of state lawmakers in the event of election disputes. In Washington, a liberal-leaning city where some 95 per cent of voters chose Mr Biden, crowds gathered beyond the new White House security fence in a celebratory mood, playing the Los del Rio’s Spanish dance classic Macarena and other lively tunes. Elsewhere, hardcore Trump supporters have rallied outside vote-counting stations in Michigan, Arizona, Pennsylvania and other battleground states, echoing the president’s complaint of irregularities and demanding to monitor the process inside. Two men armed with an AR-15 assault rifle and other military-style gear were arrested at a Philadelphia counting centre, where they reportedly said they were trying to “straighten out” the tally process inside. A pro-Trump Facebook group called Stop the Steal was created on Wednesday and quickly amassed hundreds of thousands of followers, who shared posts about voting fraud. It was shut down by the tech giant’s administrators after 22 hours. Mr Trump is trailing his Democratic challenger Joe Biden in Pennsylvania, evada, Georgia and other key states that make it unlikely he can amass the 270 electoral college votes he needs to keep his job. In a series of bad omens for Mr Trump, his long-standing media allies Fox News, the <em>New York Post</em> and a number of Republican heavyweights distanced themselves from the 45th president's unfounded claims of voting fraud. Fox anchor Bret Baier fact-checked Trump after he took to a White House podium Thursday to claim the election was fraudulent and that he was being cheated. “We have not seen the hard evidence,” Baier told viewers. As Biden took the lead in the Pennsylvania vote count for the first time, 'Fox & Friends' - a Fox show that routinely praises the president - was airing a segment about Trump increasing his support among some minority voters during the election. A <em>New York Post</em> headline described a "Downcast Trump" making "baseless election fraud" claims in his address from the White House on Thursday night and treated a victory for Mr Biden as a near-certainty. Fox News, another outlet owned by media baron Rupert Murdoch, angered many Republicans on Wednesday when it projected Mr Biden would win in Arizona — a state Mr Trump needed to keep his White House dreams alive. Meanwhile, prominent figures such as John Bolton, the president’s former National Security Adviser, and Republican lawmakers from as far afield as Texas and Illinois, bashed Mr Trump for not accepting the still-unfolding results of the November 3 election. Mr Bolton, who left the administration acrimoniously, hit out at his former boss and compared him unfavourably to Abraham Lincoln. “All candidates are entitled to pursue appropriate election-law remedies if they have evidence supporting their claims,” Mr Bolton said on Twitter. “They should certainly not lie. The first Republican president was called "Honest Abe" for a reason.” Adam Kinzinger, a Republican congressman from Illinois, rejected Mr Trump’s call for a halt to vote-counting in some battleground states and urged the president to back up his voter-fraud claims with evidence. “If you have legit concerns about fraud present EVIDENCE and take it to court,” Mr Kinzinger wrote on Twitter. “STOP Spreading debunked misinformation... This is getting insane.” Will Hurd, a Republican congressman from Texas, also turned on the president, accusing him of “undermining our political process & questioning the legality of the voices of countless Americans without evidence”. “It undermines the very foundation this nation was built upon,” Mr Hurd said on Twitter. Other Republican heavyweights, such as House minority leader Kevin McCarthy and Lindsey Graham, a senator from South Carolina, have continued to back the president and repeat his unfounded allegations of voting fraud. Others discussed what Mr Trump would do once he leaves the White House in January, assuming that Mr Biden wins and the president’s raft of electoral legal challenges and an appeal for US Supreme Court intervention fail to gain traction. Speaking at the Institute for International and European Affairs on Friday, Mick Mulvaney, the former acting White House chief of staff, said Mr Trump would “likely” run again in 2024 if he loses the November 3 election and would “absolutely” stay in politics. Others questioned whether a post-presidency Mr Trump would struggle to settle debts on his property empire or face investigation or prosecution for possible crimes involving obstruction of justice or related to his often-queried tax returns. “If Biden wins, Trump’s lame-duck period could be more tumultuous than ever,” Ian Bremmer, a commentator and founder of a political risk consultancy, the Eurasia Group, said on Twitter. “Facing legal troubles, Trump could opt to self-pardon, a move with no precedent in American history.”