Colorado’s new gun laws are coming to the fore again, as a lawsuit to overturn them opens on Monday in federal court.

Almost all of Colorado’s elected county sheriffs spearheaded the suit, saying new measures requiring universal background checks and limiting the size of ammunition magazines are both unconstitutional and unenforceable.

They join nearly two dozen other plaintiffs, including individuals, for-profit companies and nonprofit organizations. They include Magpul Industries, which makes 30-round magazines that are no longer legal to sell in Colorado, and the Colorado Farm Bureau, which represents the rights of ranchers and promotes rural values.

Magpul is in the process of moving out of Colorado in protest, relocating its operations in Texas and Wyoming. Other gun businesses have done the same.

The new gun laws were the most divisive legislation in recent memory, passed last year by the Democratic-controlled state legislature amid pressure from national groups on both sides of the issue. Even Vice President Joe Biden got involved, phoning Democratic lawmakers to urge passage while bills were being debated on the floor of the state Senate.

They also led to the state’s first-ever recall elections against state legislators, as former Senate President John Morse and former Sen. Angela Giron were kicked out of office.

A third Democratic senator resigned rather than face recall, which, if she’d lost, would have tipped the balance of power in the Senate to Republicans.

The gun control laws have resulted in calls for boycotts among hunting groups and the cancellation of some shooting competitions. They also were among the factors cited by commissioners in 10 counties that sought to secede from Colorado to form a new state.

During and after the debate on the gun laws, Colorado was ground zero in the fight over gun control following mass shootings at Sandy Hook Elementary School in Connecticut and at a movie theater in Aurora.

The National Rifle Association lobbied against the bills and helped in the recall efforts. Mayors Against Illegal Guns, a group founded by former New York City Mayor Michael Bloomberg, dumped money into the effort to prevent Morse and Giron from being recalled.

Gov. John Hickenlooper is named as a defendant in the lawsuit, which is expected to be heard in court for the next two weeks.

The new laws have been in place since last July, but no one is believed to have been charged with violating them. Plaintiffs to the lawsuit say that’s because the laws are impossible to enforce. Many sheriffs have said they’re not trying to enforce them because they consider the measures to be unconstitutional.

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