Democratic Maine Gov. Janet Mills said Monday she will allow one of a final pair of gun safety bills — a waiting period for gun purchases — to become law without her signature in the wake of the Lewiston mass shooting.

The governor announced that she would let a 10-day period pass without signing or vetoing the 72-hour waiting period bill, allowing it to go into effect without action. The law will go into effect this summer.

The governor also said Monday she has vetoed a ban on bump stocks that would have applied to a device that can be added to a semiautomatic rifle to allow it to fire like a machine gun. A gunman used a bump stock during the 2017 Las Vegas shooting, in which 60 people were killed and 869 people injured.

The 72-hour waiting period for gun sales drew fierce opposition from Republicans who said it would infringe on the rights of people who want to exercise their constitutional right to buy a gun. Maine hunting guides said that it also could crimp gun sales to out-of-state hunters who come to Maine for short excursions and buy a gun while visiting the state.

Mills said she is allowing the waiting period to become law with "caveats and concerns," and that steps to shepherd it along will follow, such as tasking the state's attorney general and public safety commission to monitor constitutional challenges over waiting periods that are playing out elsewhere in the country.

"This is an emotional issue for many, and there are compelling arguments for and against," Mills said in a statement.

The bills were among a number of actions taken by lawmakers after the deadliest shooting in state history, in which an Army reservist killed 18 people and injured 13 more at a bowling alley and at a bar and grill on Oct. 25 in Lewiston. The shooter was later found dead by a self-inflicted gunshot wound.

Mills said she vetoed the bump stock proposal because despite its "well-meaning nature" she felt the language of the bill and the way it was developed "create the risk for unintended mistakes."

The governor already signed a bill that she sponsored to strengthen the state's yellow flag law, boost background checks for private sales of guns and make it a crime to recklessly sell a gun to someone who is prohibited from having guns. The bill also funds violence-prevention initiatives and funds mental health crisis receiving centers.

Lawmakers never voted on a so-called red flag bill. Red flag laws, which have been adopted by more than 20 states, allow a family member to petition to have someone's guns removed during a psychiatric emergency.

The state's yellow flag law differs by putting police in the lead of the process, but the law was updated to allow police to ask a judge for a warrant to take someone into protective custody.

That removes a barrier of police meeting with a person to assess whether protective custody is needed, something that came into play when the Lewiston gunman refused to answer his door during a police welfare check more than a month before the shootings. The officer said no crime was committed and he didn't have authority to force the issue.