JEFFERSON CITY, Mo. • Setting up an election-year showdown with the Legislature, Gov. Jay Nixon vetoed on Wednesday a bill that would have required a 72-hour waiting period for abortions in Missouri.

Nixon said the bill’s lack of an exception for victims of rape and incest was a “glaring omission” that was “wholly insensitive to women who find themselves in horrific circumstances.”

But even if the bill had contained such an exception, he would have vetoed it, Nixon said in unusually sharp criticism of an abortion bill.

Tripling the current 24-hour waiting period “serves no demonstrable purpose other than to create emotional and financial hardships for women who have undoubtedly already spent considerable time wrestling with perhaps the most difficult decision they may ever have to make,” the governor, a Democrat, said in his veto message.

The measure would have made Missouri the third state nationally to require a 72-hour waiting period, along with South Dakota and Utah. Utah’s law includes an exception for victims of rape and incest, and people under age 14.