Washington - Fanning the flames of GOP discord, US President Donald Trump accused Republican congressional leaders on Thursday of botching efforts to avoid an unprecedented default on the national debt."Could have been so easy-now a mess!" Trump tweeted.The president's sharp words underscored the perilous state of play as Congress is without a clear plan to take care of its most important piece of business: If it does not increase the nation's $19.9 trillion borrowing limit, the government could be unable to pay its bills, jarring financial markets and leading to other harsh consequences.Trump unleashed his latest criticism of the GOP's congressional leadership in a series of morning tweets that also included a rebuke of majority leader Mitch McConnell for his inability to get the Senate to repeal the Obama health care law.The harsh posts were fresh evidence of the president's fraying relations with fellow Republicans just when the White House and Capitol Hill most need to be working in sync.StrategyCritiquing GOP legislative strategy, Trump tweeted that he had asked McConnell and House Speaker Paul Ryan to attach the legislation increasing the borrowing limit - a toxic vote for many Republicans - to popular military veterans' legislation that he recently signed.The idea was floated in July but never gained steam in Congress.Trump said that because legislators didn't follow that strategy, "now we have a big deal with Dems holding them up (as usual) on Debt Ceiling approval".Republicans control both Congress and the White House, placing the burden on them to ensure the government doesn't default.In the past, Democrats largely provided the votes for debt limit increases.The Treasury Department has said the debt ceiling needs to be raised by September 29 to avoid potential default on government obligations including Social Security and interest payments.House Speaker Paul Ryan, playing down Trump's notion of a debt limit "mess", said flatly that Congress would "pass legislation to make sure that we pay our debts."I'm not worried that's not going to get done because it's going to get done," he said during an appearance in Washington state.BroadsidesMcConnell likewise said earlier in the week that there was "zero chance, no chance, we won't raise the debt ceiling".The president's latest broadsides against members of his own party came one day after the White House and McConnell issued statements pledging to work together.After Trump's latest incendiary tweets, both sides tried again on Thursday to tamp down talk of escalating tensions.Ryan, speaking to Boeing employees in suburban Seattle, said he and Trump have "different speaking styles", but they are in "constant contact" on the policy agenda."For me it's really important the president succeeds, because if he succeeds then the country succeeds," Ryan said.White House press secretary Sarah Huckabee Sanders insisted the president's relationships with GOP leaders "are fine".For all of that conciliatory talk, the evidence of mounting friction between the president and the Republican party is growing.Arizona Senator Jeff Flake said in an interview with Georgia Public Broadcasting on August 23 that the president was "inviting" a 2020 presidential primary challenge because he was only cultivating the GOP base of voters.Growing riftTrump has labelled Flake as "weak" and "toxic" on Twitter.Maine Senator Susan Collins, a Republican who has been critical of the president, told MSNBC this week it was "too difficult to say" if Trump would be the party's presidential nominee in 2020.The growing rift between congressional Republicans and Trump could make it more difficult for the White House to advance its agenda.The White House and congressional Republicans have yet to engage in serious negotiations to address the debt ceiling or stopgap legislation needed to avert a government shutdown when the fiscal year ends on September 30.Trump is expected to hold meetings with congressional leaders after the Labor Day holiday.