SIOUX FALLS, S.D. — House Speaker Mark Mickelson is pursuing a 2018 ballot measure that aims to ban out-of-state contributions to initiative groups after ballot question campaigns brought in millions of dollars from across the nation last election cycle.

The Republican lawmaker said this week that supporters are tired of people who don’t live in South Dakota using the state to test policy ideas that they want to bring elsewhere. A similar bill capping out-of-state contributions failed in the state Legislature this year, and experts have said such measures are unlikely to survive a legal challenge.

“The special interests in Pierre succeeded in killing this bill in Senate committee, so we’re going to go around the special interests and directly to the people,” Mickelson said.

The initiative would prohibit contributions to South Dakota ballot question committees from nonresidents, out-of-state political committees and entities that haven’t filed with the Secretary of State’s office for the preceding four years.

Since Election Day 2016, when voters decided 10 ballot measures, Republicans have frequently complained about outside interests experimenting with South Dakota’s laws and constitution. Out-of-state donors pumped over $10 million into campaigns for or against the state’s questions.

A California billionaire whose sister was killed by a stalker ex-boyfriend bankrolled an amendment that established constitutional rights for crime victims. A Massachusetts group funded a transformative government ethics initiative that was on the books until lawmakers quickly repealed it. And a car title lender based in Georgia with locations in South Dakota tried unsuccessfully to amend the state constitution to allow unlimited interest rates.

A spokesman for Republican Gov. Dennis Daugaard said in an email that he agrees with Mickelson’s proposed ballot measure, but generally doesn’t plan to be very active in 2018 initiative campaigns.

“There’s a lot of support for this measure,” Mickelson said.

But, the likelihood the ballot initiative would be upheld in a court challenge is “slim-to-none,” according to Paul S. Ryan, a vice president at the Washington watchdog Common Cause, which opposes big money in politics.

The ballot measure proposal conflicts with a 1981 U.S. Supreme Court decision that declared that contributions to ballot measure committees can’t be limited under the First Amendment, Ryan said.

“People in other states haven’t really pursued this as a viable reform,” Ryan said. “It is pretty rare to see people pursue a reform that the Supreme Court has said is unconstitutional.”

Ben Lee, state director of Americans for Prosperity-South Dakota, said the group is concerned with the proposal because it would limit free speech.

“I believe that citizens should have the right to support the causes and the issues that they believe in without fear of harassment and without unconstitutional restrictions,” Lee said.

Mickelson also separately wants to ask voters to raise tobacco taxes to make state technical institutes more affordable. Supporters would have to submit nearly 14,000 valid signatures for each initiative to the secretary of state by November 2017 to put them before voters in 2018.

The Argus Leader first reported details of the initiatives.