In the waning days of the 2014 elections, Chris Christie arrived in Ohio to campaign for his fellow Republican, John Kasich. At a rally for over 700 people in the town of Independence, the Ohio governor said of his New Jersey counterpart that, “among all the governors, he’s my best friend.” The audience let out a collective “awww.” The two were shown the next day on the front of the Cleveland Plain Dealer, shoulder-to-shoulder, beaming.

A few weeks later, Christie was back in the Midwest, this time campaigning for Wisconsin Governor Scott Walker, who was locked in a tight re-election battle.

This time though, the reaction was more “ooooooh,” rather than “awwww.”

“Chris is coming because he asked if he could come,” Walker said when asked about the visit. “We weren’t going to say no. We’re not looking for surrogates.”

The Republican race for the GOP nomination is in its earliest days. And for the most part, the candidates have observed Ronald Reagan’s 11th Commandment: “Thou Shall Not Speak Ill of Any Republican.”

That is, except for Walker.

Four days after winning re-election last November, Walker took shots at Kasich, who had bucked conservative orthodoxy by pushing through a Medicaid expansion, citing St. Peter and his Christian faith.

“It’s probably not fair to ask the son of a preacher to use biblical metaphors. My reading of the Bible finds plenty of reminders that it’s better to teach someone to fish than to give them fish if they’re able,” Walker said at the time. “Caring for the poor isn’t the same as taking money from the federal government to lock more people into Medicaid.”

Walker has been busy tossing these types of bricks for a while now. When asked about Jeb Bush, for example, he told a New Hampshire interviewer, “To beat a name from the past, we need a name from the future.” At CPAC, Walker told the crowd how he, “the son of a small-town preacher,” visited Independence Hall in Philadelphia as an adult because he never had a chance to go as a kid. “That was a double-knock on Bush, the son and brother of former presidents, who once chaired the National Constitution Center—down the street from Independence Hall,” The Washington Post reported.

In fact, Walker has been knocking his fellow Republicans for years. During the 2012 campaign, he regularly criticized Mitt Romney’s campaign, saying that Romney was too cautious and needed to show “fire in the belly.” Back in 2013, he was publicly suggesting that the next Republican nominee should be a governor before Congressman Paul Ryan, his fellow Wisconsinite and Romney’s running mate, had announced whether he would run.

As his polls showed his own re-election a toss-up, Walker and his allies went public with criticism that the Republican Governors Association was failing to send enough donations to Wisconsin—even though the RGA, which Christie chaired, had spent $8 million on his re-election, on top of nearly $9 million the group had spent two years before to help him fend off a recall.

“[Walker] is always in campaign mode—always,” said one Ohio Republican political operative, who added that some Walker allies were reaching out to political operatives in Ohio even before the midterms were over.

An aide to another Republican governor said, “The Republican class of governors in 2010, I always felt like we were already pretty much working together and on the same team. Walker seemed to view everybody else as a potential adversary.”

Many Republicans see Walker’s willingness to throw elbows as the natural outgrowth of someone who has been climbing up the greasy political pole since he was 22, first as an assemblyman, then as Milwaukee County executive and governor.

“He is an aggressive politician, I don’t think there is any doubt about that,” said Jeff Mayers, editor of WisPolitics.com, which covers the state’s political scene. “If there is an opening, he is not afraid to go in there and fill it.”

Mayers said he noted a shift in Walker after he prevailed in his fight with the public-sector unions and then became the first governor in history to survive a recall. Those battles, he said, “hardened his edge. He has always been aggressive, but I think he saw then that he could succeed without getting much more than 50 percent of the vote.”

But other Wisconsin politicos say that Walker has long operated at his own political speed.

David Riemer ran against Walker when he sought re-election as Milwaukee County executive in 2004. In that race, the Walker campaign ran ads accusing Riemer of engineering a city pension settlement that cost taxpayers millions of dollars. The pension settlement actually saved the county some $20 million, Riemer said, a fact that the city comptroller and city attorney backed up. According to a newspaper account at the time, Walker refused to pull the spots, even as “he again conceded that the ad’s assertion is not correct as stated.”

“What kind of person admits that they are wrong but won’t change what they are doing,” asked Riemer when reached by phone this week. “His main goal has been to get into higher office and then use that to get into even higher office.”

Other candidates have much been more hesitant to go on the attack. When Jeb Bush was asked, for example, about Walker’s recent flip-flops on immigration, he deflected and deflected until reporters followed him out of a campaign stop and told him that Walker had admitted changing his opinion on the issue.

“He’s changed his views on immigration, yes,” Bush, said, concurring with Walker’s own opinion.

When Marco Rubio was asked about Bush, he declined to criticize him, calling him “a very credible candidate” and praising his fundraising abilities. When Rand Paul entered the presidential race, Ted Cruz called him “a good friend” whose entry into the race will “help make us all stronger.” Mike Huckabee is on the record with high praise for Rick Perry and one-time candidate Mitt Romney.

If any of the GOP contenders seem willing to push back Walker’s comments so far, it is Kasich, who, while he may not be the son of a preacher like Walker, wanted to be a priest when he was a boy and whose parents were killed in car accident by a drunk driver in 1987. Often in profiles, Kasich is portrayed as growing most animated when he is compared to the Midwestern governor, who has shot far ahead of him in early state polls.

When, for example, a New York Times reporter mentioned that many people think Walker is more conservative, Kasich “bolted upright. ‘I think I have the right to define what conservatism is,’” he roared, launching an 11-minute defense of his record. And days after Walker’s biblical comments, Kasich tore into Walker while on stage beside him at an RGA event in Washington, D.C.

It remains to be seen how much all of this matters, whether Walker will have a head start in defining his rivals or whether he will be seen as a petulant elbow-thrower.

If his rivals don’t like it, though, Dave Carney, a former adviser to Rick Perry and Newt Gingrich, said they should “buy a helmet.”

“With the amount of money in this primary, we aren’t going to just see elbows being thrown but knees, fists, and probably ballistic missiles at some point,” he said.