Florida is not the only state trying to stop eligible people from voting. Georgia passed a law in 2005 that made voters pay for their voter ID cards — a modern poll tax. The fee was eventually removed, but the law could still block as many as 300,000 registered voters without the right ID from casting ballots. In 2004, Ohio ordered counties to throw out voter registration forms that were not on thick enough paper.

It is chilling to think that state legislators and election officials would intentionally try to make it harder for Americans to vote, but they always have — with poll taxes, literacy tests and gerrymandering. There was a time when the Supreme Court regularly struck these restrictions down. In 1966, it held Virginia’s $1.50 poll tax unconstitutional. In 1972, it ruled that Tennessee’s one-year residency requirement for voting violated the Constitution.

Now the Supreme Court has switched sides. This week, it upheld a harsh Indiana voter ID law that could disenfranchise many poor, elderly and student voters. The ruling will make it even easier for other states to block voters’ access to the ballot box.

If the courts won’t protect voters, Congress has to. The Constitution, in Article 1, Section 4, gives Congress broad authority to set the rules for federal elections. It should use this power to set minimum voting rights standards that would apply nationwide and ensure that all eligible Americans could vote.

Voter registration rules are the place to start. Federal law should hold organizations like the League of Women Voters harmless if they make good-faith mistakes while registering people. There should be a federal voter registration form, usable in any state, and uniform regulations so Ohio could not throw out forms based on paper thickness and Florida could not bar voters, as it now does, from fixing small errors on a form within a month of an election.

Congress should also regulate voter challenges at the polls. Parties and candidates often use bad-faith challenges as a dirty trick — to intimidate voters or to slow down voting in certain neighborhoods. Senator Sheldon Whitehouse, Democrat of Rhode Island, has a good bill that would require challengers who are not election officials to sign an affidavit stating why they believe a specific voter is not eligible.

Ballot formats should be standardized nationally rather than left to the often bad judgment of local officials. Palm Beach County’s butterfly ballot, which apparently changed the outcome of the 2000 presidential election, got a lot of attention, but there are confusing ballots in use across the country.

The patchwork of state ID laws should be replaced by a single standard that allows people to present any of an array of identification, including college IDs, and permits voters to sign an affidavit if they do not have ID.

There are many other problems that need to be fixed. Some states’ rules for provisional ballots — used when election officials cannot find a voter’s name on the rolls — are clearly designed to disqualify a large number of ballots from eligible voters.

Congress also needs to set a minimum standard for the number of voting machines per voter and ensure that states allocate them equitably. There were widespread reports in Ohio in 2004 of voters in poor, black neighborhoods waiting hours to vote while white neighborhoods had no lines. At Kenyon College, students waited up to 10 hours.

Good reform bills have been introduced in Congress, including ones backed by Senators Barack Obama and Hillary Rodham Clinton. But they have faced strong partisan opposition, and lobbying from influential state and local election officials. Critics of reform make the specious argument that states have the right to set the rules for federal elections. The founders, when they wrote the Constitution, said otherwise.