A Times poll shows large majorities back spending on roads, ports, broadband and more. But Republicans aim to make corporate tax increases the issue.President Biden’s $2.3 trillion infrastructure plan has yet to win over a single Republican in Congress, but it is broadly popular with voters nationwide, mirroring the dynamics of the $1.9 trillion economic aid bill that Mr. Biden signed into law last month.The infrastructure proposal garners support from two in three Americans, and from seven in 10 independent voters, in new polling for The New York Times by the online research firm SurveyMonkey. Three in 10 Republican respondents support the plan, which features spending on roads, water pipes, the electrical grid, care for older and disabled Americans and a range of efforts to shift to low-carbon energy sources.That support is essentially unchanged from a month ago, when SurveyMonkey polled voter opinions on a hypothetical $2 trillion Biden infrastructure package, despite Republican attacks since the president outlined his American Jobs Plan in Pittsburgh at the end of March. And there is near-unanimous support for the plan from Democrats, whose confidence in the nation’s economic recovery has surged in the first months of Mr. Biden’s administration.“What we’ve seen with all our polling so far this year is that these proposals that the Biden administration has been rolling out have met with widespread approval,” said Laura Wronski, a research scientist at SurveyMonkey.Republican leaders hope they can ultimately turn some voters, particularly independents, against the plan by attacking Mr. Biden’s proposal to fund it with tax increases on corporations. Those increases include raising the corporate income tax rate to 28 percent from 21 percent and a variety of measures meant to force multinational corporations to pay more in tax to the United States on profits they earn or book abroad.Senior Republicans in Congress are eager to wage that fight, arguing that voters will sour on even popular spending provisions if they are offset by tax increases that could chill investment and economic growth. They have cast the corporate tax cuts that President Donald J. Trump signed into law in 2017 as a boon for the economy that would be catastrophic to reverse.“Infrastructure’s popular,” Senator Mitch McConnell of Kentucky, the Republican leader, told reporters this week. “We need to have an infrastructure bill as big as we’re willing to credibly pay for without going back and undoing the 2017 tax bill.”Mr. Biden’s aides are similarly convinced that turning voter attention to corporate taxes — and to the 2017 tax cuts, which have never polled as well as Mr. Biden’s spending ambitions — will only help them solidify their case to the public. They cast the tax increases in his plan as a necessary corrective to that law, which they say rewarded corporations without producing the investment boom Republicans promised, and as the right way to offset popular spending programs.The Republican case against corporate tax increases “doesn’t fit this economic moment,” said Heather Boushey, a member of the White House Council of Economic Advisers. “People have learned that there’s only so low you can go. And if the tax system allows America’s most profitable companies to not have to pay their fair share, that’s not in the national interest, and it’s certainly not in the interest of American workers.”Public support for the infrastructure plan isn’t quite as overwhelming as it was for Mr. Biden’s first major piece of legislation, the $1.9 trillion stimulus package that sent $1,400 checks to most Americans. That bill won the support of 72 percent of Americans, including 43 percent of Republicans, in a February poll, also conducted by SurveyMonkey.But support for the infrastructure plan is broad-based. The proposal draws majority approval from adults across virtually every social and demographic category: men and women, young and old, college-educated and not.Individual components of the plan are even more popular. Sixty-seven percent of respondents said they supported increased federal spending on mass transit; 78 percent supported spending on airports and waterways, and on improving broadband internet access; and 84 percent supported money for highways and bridges. The latter two categories won majority approval even from Republicans.“Republicans don’t support the American Jobs Plan over all, but there are some elements of it that they actually love,” Ms. Wronski said.The Times survey did not ask about other components of Mr. Biden’s plan, such as those focusing on the environment, health care and education. But other polls have generally found support for those proposals as well, although in some cases by narrower margins.Mr. Biden has said he will pay for the bulk of his plan by partly reversing the corporate tax cuts passed by his predecessor, and most polls routinely show that the public favors raising taxes on large corporations.But there may be room for the Republicans’ tax argument to win over some independents. According to the SurveyMonkey findings, among independents who don’t have a strong position on the infrastructure plan, 29 percent say the tax increases would make them less likely to support it. Just 16 percent of that group says the higher taxes would make them more likely to support the plan.A survey released Wednesday by Quinnipiac University found somewhat lower overall support for the infrastructure plan, but also found that the plan was more popular when it was funded by raising taxes on corporations.Joel Slemrod, a University of Michigan economist who studies tax policy, said it wasn’t clear whether other ways of paying for infrastructure spending — including not paying for it and instead adding to the deficit — would be more popular.“A pretty good majority of people think that corporations and also rich people don’t pay their fair share,” he said.The polling helps to underscore the emerging political challenge for Republicans, who have roundly praised infrastructure spending in the abstract but opposed the scope of Mr. Biden’s proposal and the tax increases that would fund it.“It’s how we define it, how we pay for it, that gets everybody all twisted sideways,” said Senator Lisa Murkowski, Republican of Alaska. “But I think we must present an alternative if you think this is too big. How would we pare it down? How would we define it? How will we pay for it?”Some Republicans are floating the possibility of putting forward a counterproposal that addresses more traditional infrastructure needs and removes the corporate tax increases. Senator Shelley Moore Capito of West Virginia suggested that such a proposal could be between $600 billion and $800 billion.“I think the best way for us to do this is hit the sweet spot of where we agree, and I think we can agree on a lot of the measures moving forward,” Ms. Capito said on CNBC on Wednesday. She suggested that Democrats save proposals with less bipartisan support for the fast-track budget reconciliation process, which would allow the legislation to pass with a simple majority.“If there are other things they want to do — they being the Democrats or the president — want to do in a more dramatic fashion that can’t attract at least 10 Republicans, that’s, I think, their reconciliation vehicle,” Ms. Capito added.But several liberals have signaled a reluctance to whittle down Mr. Biden’s plan, with Senator Bernie Sanders of Vermont, the chairman of the Senate Budget Committee, telling reporters that the tentative price range “is nowhere near what we need.”The Biden administration is rolling out its infrastructure plans from a position of relative strength. Voters generally give Mr. Biden high marks for his performance in office, at least in comparison with Mr. Trump’s consistently low approval ratings, and Americans are becoming more optimistic about the economy in particular. Measures of consumer sentiment have been rising in recent months; SurveyMonkey’s consumer confidence index, which is based on five questions about people’s personal finances and economic outlook, rose in April to its highest level in six months.But views of the economy remain starkly divided along partisan lines. Confidence among Democrats jumped when Mr. Biden was elected and has continued to rise since. Republicans, who had a rosier view of the economy than Democrats throughout Mr. Trump’s time in office, have turned pessimistic since the election.About the survey: The data in this article came from an online survey of 2,640 adults conducted by the polling firm SurveyMonkey from April 5 to 11. The company selected respondents at random from the nearly three million people who take surveys on its platform each day. Responses were weighted to match the demographic profile of the population of the United States. The survey has a modeled error estimate (similar to a margin of error in a standard telephone poll) of plus or minus three percentage points, so differences of less than that amount are statistically insignificant. More