A majority of the U.S. Supreme Court appeared poised Wednesday to reverse or limit a line of precedents with roots — some more than a century old — that has allowed the government to ban corporate and union expenditures in election campaigns.

After an extraordinary 90 minutes of oral argument in Citizens United v. Federal Election Commission , it seemed likely that the court, swayed by arguments in favor of First Amendment rights for corporations, was ready to embark on a new course that critics say could unleash a flood of corporate wealth into elections that are already awash in more regulated kinds of campaign spending.