Mike Pence is going right after Donald Trump in Arizona

(CNN) - Mike Pence seems to have decided that the only way past Donald Trump is through Donald Trump.

Unlike many of Trump's would-be 2024 challengers, his former vice president is issuing a direct challenge by endorsing against him in critical races in states that were hotly contested in 2020.

Pence's latest move is an endorsement of Republican Karrin Taylor Robson in the Arizona governor's race.

"As Arizona Democrats pursue the reckless Biden-Harris agenda, Karrin Taylor Robson is the only candidate for Governor that will keep Arizona's border secure and streets safe, empower parents and create great schools, and promote conservative values," Pence said in a statement announcing the endorsement.

(Robson has also been endorsed by outgoing Arizona Gov. Doug Ducey, who has drawn Trump's ire for his refusal to overturn the 2020 election results in the state.)

That move puts Pence in direct opposition to Trump, who is supporting former local TV anchor Kari Lake in the state's August 2 primary. "Few can take on the Fake News Media like Kari," Trump said in announcing his endorsement last fall.

Lake has been one of the highest-profile backers of Trump's false election fraud claims.

She has gone as far as to say it is "disqualifying" that Robson does not believe the election was stolen from Trump.

In an interview Sunday with CNN's Dana Bash, Ducey, who co-chairs the Republican Governors Association, was blunt in his assessment of Lake: "Kari Lake's misleading voters with no evidence," he said.

The move by Pence to endorse Robson is rightly understood then not as simply a rejection of a Trump-backed pick, but an attempt to affirm that the 2020 election was, in fact, free and fair.

Pence and Trump are scheduled to hold dueling rallies on behalf of their preferred candidates in the state on Friday.

And this isn't the first time Pence has done something like this.

He backed Georgia Gov. Brian Kemp in the spring, putting him, again, on the opposite side of Trump, who had recruited former Sen. David Perdue into the Republican primary.

(Kemp, like Ducey, was repeatedly attacked by Trump for his refusal to overturn the 2020 results in his state.)

Campaigning with Kemp the day before the May 24 primary, Pence was clear about what he believed the vote meant.

"When you say yes to Gov. Brian Kemp tomorrow, you will send a deafening message all across America that the Republican Party is the party of the future," Pence said.

Kemp crushed Perdue by more than 50 points.

It's a remarkable turn of events that Pence, more so than any other Republican considering the 2024 race, has emerged as the one willing to stand up to Trump and his election lies.

(Florida Gov. Ron DeSantis, for example, isn't getting involved in contested primaries outside of his state.)

After all, Pence spent four years as essentially Trump's wingman. At seemingly every bill signing, Pence was standing behind Trump, giving him an "attaboy, boss."

At speech after speech in the White House, Pence was in the background, nodding along to the points Trump made.

At one Cabinet meeting in 2017, Pence praised Trump every 12 seconds -- for three minutes straight.

So, what happened?

Well, January 6 happened.

Trump engaged in an extended pressure campaign to try to get Pence to overturn the 2020 election results.

And as Cassidy Hutchinson, a former aide to White House chief of staff Mark Meadows, testified before the House select committee investigating January 6, Trump was apparently approving of the chants of "Hang Mike Pence" from the rioters storming the US Capitol that day.

That, you would think, changes someone.

Pence now seems to understand that the only way he has a political future in the GOP is to prove -- through a series of steps -- that Trump is less powerful than he is being made out to be.

The Kemp endorsement -- and the governor's primary victory -- put a crack in the Trump wall. Pence hopes Arizona will make that crack even bigger.