If recent history is any guide, this fall’s presidential election will be marred by vote suppression and cynical dirty tricks. Congress still has time to stop some of the worst offenses. The Senate is considering two bills, one to outlaw so-called vote caging and another to rein in duplicitous robo-calls. Congress should pass both bills well before Election Day.

Vote caging is a little-known but pernicious technique. Political operatives mail letters to voters, targeting areas where the opposing party is strong. If a letter is returned as undeliverable, the voter’s name is put on a list to be challenged at the polls. The challengers try to persuade election officials not to let the person vote, or only to let them cast a provisional ballot. Some voters end up disenfranchised. No matter how the challenges turn out, they often create confusion and long lines, reducing turnout in the targeted precincts.

Minority voters have been especially victimized. In an infamous case in Louisiana, a Republican political operative boasted that a vote-caging program “could keep the black vote down considerably.” Vote caging is sometimes defended as a way of removing ineligible voters from the rolls. But there are many reasons letters are returned, including errors in names and addresses, which are common on direct-mail lists.

Senator Sheldon Whitehouse, Democrat of Rhode Island, has sponsored a good bill that would require operatives to present better evidence when they challenge a voter’s eligibility, such as verifiable proof that a prospective voter has moved or died. The bill would not deter legitimate efforts to keep ineligible people from voting, but it should greatly reduce the use of voter challenges as an Election Day dirty trick.