A polling place in St. Charles, Mo., on April 2. (David Carson/St. Louis Post-Dispatch via AP)

LAST NOVEMBER, Missouri was one of a handful of states in which voters decided to limit politicians’ power over redistricting, the decennial process in which political boundaries are drawn, because allowing politicians to choose their own voters has become an increasingly corrupt exercise. Now, Missouri Republicans, who have a lock on the state’s legislature and stand to lose some control under the new system, are trying to roll back the reform, insisting that voters were tricked into approving it.

Their cynical maneuver represents another new low in the steady Republican undermining of democracy through false claims of voter fraud, restrictions on voting and other tactics. The Supreme Court, deliberating on whether politicians can be trusted not to deprive voters of their rights through extreme gerrymandering, should take note.

Missouri voters approved a plan that would rely on a professional state demographer to draw lines that would not be warped in favor of one party or another. It was not perfect, but it was better than what Republicans wanted: a system in which the parties have more control — and in which partisan fairness is not a focus. More to the point: Once Missourians embraced a different approach, the debate should have been over. Nevertheless, with supermajorities in both chambers of the statehouse, the GOP can ram the plan through.

The Supreme Court is considering whether courts should finally referee disputes over partisan gerrymandering, as the practice has become increasingly antidemocratic. The justices seemed hesitant to involve the courts because voters appeared to be imposing curbs on gerrymandering without judicial involvement. But the experience in Missouri and other states shows that politicians will seek to undermine reforms, no matter what the voters say.

Over the years, both parties have angled for advantage in the political line-drawing process and in other areas of election administration. But Republicans have taken the practice to extremes. They heavily gerrymandered political maps in North Carolina and Wisconsin, discouraged voting among Democratic-leaning groups through a war on phantom voter fraud, limited weekend voting and closed voting places in areas where many Democrats live. Where their deck-stacking was not enough to keep them in power, they have undermined the Democrats who beat them, removing power from incoming Democratic governors and state attorneys general.

Meanwhile, as Missouri lawmakers debate their rollback, Texas Republicans are moving to treat mistakes on voter-registration forms as felony offenses that could bring jail time and to discourage people from casting provisional ballots, NPR reported. Tennessee Republicans want to heavily fine groups that turn in improperly filled-in voter-registration forms. Arizona Republicans would cut voters from the mail-in ballot rolls if they do not vote in two successive elections. All of these will help dampen the vote in a country that already suffers from low participation.

Politicians should not seek to make voting inconvenient, and they should respect election results. These points should be obvious. But apparently they are not.