Newsom, a fierce advocate of gun control, said his proposed 28th Amendment has four prongs: It would institute what he called a "reasonable" waiting period for all gun purchases, ban so-called assault rifles throughout the country, require universal background checks and raise the minimum age to buy a firearm to 21.
"Hey Governor Newsom, The 2nd Amendment already exists—we don’t need a 28th," tweeted House Speaker Kevin McCarthy. "But what we do need is for Presidential aspirants to stop pushing their extreme positions nationally."
To which Newsom promptly replied, "Hey Kevin, What we need is you to own up to the fact that you represent a district with the highest murder rate in our state -- and you’re doing nothing to address it."
Earlier Thursday, Mississippi Governor Tate Reeves tweeted to Newsom that he was willing to debate him on his 28th Amendment proposal.
"Can’t wait for you to defend the fact that Mississippi has the highest gun violence death rate in the nation…. (377% higher than California’s, by the way)," replied Newsom. "You can’t be serious."
Newsom said he believes he can be successful because a majority of Americans say they want stricter gun laws.
There have been 26 mass killing incidents nationally 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.
"@GavinNewsom's latest publicly stunt once again shows that his unhinged contempt for the right to self-defense has no bounds," tweeted the National Rifle Association. "California is a beacon for violence because of Newsom’s embrace of policies that champion the criminal and penalize the law-abiding. That is why the majority of Americans rightfully reject his California-style gun control."
Newsom will run his efforts through his new political committee, Campaign for Democracy. He ended his last campaign with more than $16 million left in his political account, some of which will be spent on his new effort.
The Associated Press contributed to this report.
Sara Sedillo is a digital reporter for KTVU. Email Sara at firstname.lastname@example.org.