Miami - Hillary Clinton is turning to a major health issue in the battleground state of Florida with a visit on Tuesday to a Miami neighbourhood dealing with the first US outbreak of the Zika virus.Clinton will call on Republican congressional leaders to summon lawmakers back to Washington from their summer recess and pass emergency funding for the Zika response. She wants immediate action to either pass stalled legislation or craft a new bipartisan compromise, according to aides briefed on her plans.The Democratic presidential nominee will be urging the action as she tours the Borinquen Medical Center, a health clinic close to the Wynwood area where 16 non-travel related cases of Zika have been diagnosed.It's an issue that could affect votes in this crucial swing state where she has held a small advantage in recent polls. So far, Trump has not addressed the Zika response in depth, though he told a Florida television station last week that Governor Rick Scott, a Republican, "really seems to have it under control in Florida".Until this month, the only known Zika cases in the United States were in people who had recently travelled to Latin America or the Caribbean. Federal officials last week warned pregnant women to avoid the Miami neighbourhood and a 2.5km² area around it.Lawmakers left Washington in mid-July for a seven-week recess without approving any of the $1.9bn that President Barack Obama requested in February to try to develop a vaccine and control the mosquitoes that carry the virus.Obama, Clinton and Democrats blame Republicans for politicising the legislation by adding a provision to a $1.1bn take-it-or-leave-it measure that would have blocked Planned Parenthood clinics in Puerto Rico from receiving money.Playing politics Republicans, in turn, say the administration has not spent money that has already been provided and it's the Democrats who are playing politics in an election year.The focus on Zika comes in the midst of an economic debate between the two candidates following Trump's announcement of a retooled tax proposal including substantial tax cuts. At the same time, Trump is contending with concerns about his ability to serve as president, with a growing list of fellow Republicans deeming him unfit for the Oval Office.Maine Senator Susan Collins, a moderate long wary of Trump, became the latest Republican to announce her intent not to vote for her party's nominee. She said late on Monday in a Washington Post op-ed she'd thought "long and hard" about whether she was obligated to support the GOP nominee and decided she could not. Collins wrote that she supports neither party's nominee, though previously she's said she's open to voting for Hillary Clinton.The defection by a respected senator added to a chorus of GOP voices insisting they can't back Trump. About 50 Republican former national security officials signed an open letter calling Trump the most reckless candidate in history, prompting a counter-attack from Trump, who said the signers share blame with Clinton for making the world "a mess" and aiding the Islamic State group's formation.The renewed focus on GOP discord is not the theme Trump has hoped to emphasise, especially as fresh polls appear to show Clinton widening her lead. But Trump suggested on Tuesday there will be no dramatic change of strategy."I think it's just, you know, steadiness," Trump told Fox Business. "And it's just doing what I'm doing."A day earlier, Trump had tried in a major policy speech at the Detroit Economic Club to turn the page on a dreadful stretch in his campaign by unveiling his new tax proposal, which would reduce to three the number of income tax brackets and cut corporate taxes to 15%. Clinton quickly accused Trump of offering "super big tax breaks" to huge companies and rich people and disputed his claim that she wanted the middle class to pay more.The two candidates are headed toward a trio of televised showdowns. Late on Monday, Clinton's campaign chair announced she would take part in all three debates that the Commission on Presidential Debates is organising. Trump has said he wants to debate Clinton, but has complained that two of the debates are scheduled during NFL football games, claiming Democrats "rigged" the schedule.As Clinton continued her efforts in Florida, Trump, too, had his eye on the most competitive states. A day after campaigning in Michigan, the real estate mogul planned a pair of rallies in North Carolina.