WASHINGTON, Jan 19 (Reuters) - Conservative Democratic U.S. Senator Joe Manchin on Wednesday said he opposed changing the chamber"s rules to ease passage of a voting-rights bill, all but dooming the measure"s passage in a high-stakes vote later in the day. Manchin took to the Senate floor to reiterate his opposition to changing the filibuster rule on Wednesday, as Republicans prepared to use the 60-vote threshold to block an election reform bill Democrats insist is necessary to preserve the right to vote in the United States. He spoke as President Joe Biden, who has called the bill critical to preserving democracy, was giving his first news conference in months. "Let this change happen in this way the Senate will be a body without rules," Manchin said. "We don"t have to change the rules to make our case to the American people for voting rights." Biden told reporters on Wednesday that he had not given up hope of passing the voting-rights bill. "We"ve not run out of options yet," Biden said. Manchin joined fellow conservative Democrat Kyrsten Sinema in announcing their opposition to the rules change in Senate floor speeches. The Senate was scheduled to hold a procedural vote at about 6:30 p.m. EST (2330 GMT), which will require supermajority support to advance the voting rights legislation toward final passage. If that vote fails, as is widely expected, Senate Majority Leader Chuck Schumer has said he will move to alter the filibuster rule by vote. It was unclear when that vote would occur. With the Senate split 50-50, Democrats would need support from all of their caucus members plus a tie-breaking vote from Vice President Kamala Harris to change the chamber"s rules. "If Republicans block ... the legislation before us, I will put forward a proposal to change the Senate rules to allow for a talking filibuster," Schumer said in a floor speech earlier on Wednesday. "There are some in our caucus who believe (the filibuster) helps bring us together. I don"t see that evidence," Schumer added. Democrats say the bill is crucial to protecting the American political system as Republican-led states pass a wave of new voting restrictions, driven by former President Donald Trump"s false claims of widespread election fraud. Republicans dismiss the bill as a partisan power grab. As Republican after Republican accused Democrats of trying to usurp states" rights to administer elections, Democratic Senator Raphael Warnock said their arguments "have sounded uncannily familiar" to segregationists" opposition to civil rights legislation of the 1960s, which ultimately succeeded. Senate Minority Leader Mitch McConnell, the chamber"s top Republican, warned of a legislative "nuclear winter" if Democrats succeed in upending the 60-vote threshold. But he predicted that a slim majority of lawmakers would preserve the filibuster and turn back what he called a partisan Democratic frenzy. "The fear is false, the rage is misplaced and today factional fevers will not carry the day," said McConnell, contending that Democrats would pay a political price even for a failed attempt to overturn Senate rules. "For both groups of senators, this group will echo for generations. Before we part ways tonight, all 100 of us will have marked our legacies in permanent ink," he said. If the week ends in failure for Biden and his fellow Democrats in Congress, attention is expected to turn to a possible bipartisan effort by a small group of moderate senators to fashion narrower election rule changes. Such an effort could include new federal funding to help protect non-partisan state election workers from threats against their safety, which have been mounting since the 2020 presidential election. Also under discussion are ways to tighten the way Congress certifies presidential elections every four years. The battle over voting procedures and campaign finance reform comes against the backdrop of several Republican-controlled state legislatures stripping away some of the get-out-the-vote practices allowed in 2020 while piling on new restrictions. Their efforts have been embraced and encouraged by Trump. More than a year after his November 2020 loss to Democrat Biden, Trump has continually and falsely insisted that the election was stolen from him by widespread voter fraud. That claim has been debunked by multiple court decisions, Trump"s own Justice Department and Republican-instigated investigations. Among the practices Democrats want to turn into minimum federal voting standards are the opportunity for any registered voter to request a mail-in ballot, at least two weeks of early voting and ballot drop boxes that make voting more convenient in many areas. The Democrats" legislation also would attempt to remove partisanship from the way congressional districts are redrawn every decade. Currently, "gerrymandering" regularly tilts the field to whichever party is in power in the various states.