Gov. Gavin Newsom took to Twitter Thursday morning to announce his plans for the 28th Amendment to the United States Constitution "to help end our nation’s gun violence crisis."

"The American people are sick of Congress’ inaction," said Newsom in the tweet. "The 28th will enshrine 4 widely supported gun safety freedoms—while leaving the 2nd Amendment intact."

If enacted, the amendment will:

1) Raise the minimum age to purchase a gun to 21;

2) Establish universal background checks;

3) Create a reasonable waiting period for gun purchases;

4) Ban the civilian purchase of assault weapons.

An amendment needs a two-thirds majority vote in both the Senate and House of Representatives before it is sent to states for ratification.

With the U.S. bitterly divided over gun rights and the 2nd Amendment, the chances of recasting the Constitution to enshrine universal background checks, a waiting period to buy firearms and other restrictions into law appeared remote. A new amendment has not been added since 1992.

Newsom has denied any interest in a presidential run and is supporting President Joe Biden's reelection bid. But his proposal marked his latest maneuver in what has taken on the look like a shadow campaign as he injects himself into the national discussion on guns, abortion, immigration and other contentious issues.

He's been in a running dispute with Florida Gov. Ron DeSantis, a Republican presidential candidate, and traveled to Florida in April to criticize what he said are GOP efforts to tread on LGBTQ+ rights, weaken civil and voting rights, ban abortion and marginalize people of color. They've recently clashed after Florida picked up asylum-seekers on the Texas border and took them by private jet to California—Newsom called DeSantis a "small, pathetic man."

As of early May, the U.S. was on a record pace for mass killings, according to a database maintained by The Associated Press and USA Today in a partnership with Northeastern University. The database counts killings involving four or more fatalities, not including the perpetrator, the same standard as the FBI, and tracks the number of variables for each.

There have been 26 mass killing incidents so far this year, the most in any year so far during the period for which data has been compiled. Those incidents left 131 people dead.