In the race for the GOP nomination, heated exchanges between certain candidates have been plentiful as each candidate tries to appeal to conservative voters.

Two particular candidates who are often called friends — Jeb Bush and Marco Rubio — have avoided attacking each other in the media. That is, until recently.

Bush recently called out Rubio on his voting record, as the Florida senator has skipped voting in the Senate to campaign for the presidency.

“We should cut the pay of elected officials that don’t show up to work,” Bush said last week at an event in Iowa.

“I don’t know about you, but this idea that somehow voting isn’t important, I mean what are they supposed to do?” he asked. “They should go to the committee hearings, they should vote.”

These differentiating attacks become more vital as the the Iowa caucuses approach.

“They both try to paint themselves as conservative, but pragmatic,” said David Andersen, assistant professor of political science. “There’s not much of a difference between them.”

Bush and Rubio have many similarities: they both appeal to Latinos and speak Spanish fluently. They call Florida home and have worked together in the Florida state government.

Politically, they draw from the same donor base and many of their policies are similar. Both candidates were two of the main recipients of former Scott Walker supporters after Walker dropped out of the race late last month.

Experience is one area where Bush differs from Rubio. Bush — who is 62 years old and the son of a former president and brother to another — often points to his success of implementing conservative policies during his tenure as Florida’s governor.

Rubio doesn’t have the same level of experience as Bush, but hopes his new, energetic and fresh-faced approach can appeal to conservative voters, which is an area where Bush lacks. Donald Trump has often called Jeb’s campaign “low energy.”

“I’ve been [in Washington] four and a half years. I haven’t been there 40. I’ve been there long enough to know it’s broken, not so long that I’ve fallen in love with it,” Rubio said at an event in New Hampshire earlier this month.

The similarities between the two, along with their friendship in the past, are set to have a significant impact on the GOP race.

“The longer they both stay in the race, the more it might become an issue,” Andersen said about the possibility of their campaigns affecting their relationship.

In an MSNBC interview earlier this month, Bush was asked if he believed Rubio had the necessary leadership skills to help fix problems in the country.

“Barack Obama didn’t end up having them and he won an election based on the belief that people had that he could, and he didn’t even try,” Bush said.

Rubio and Bush have both had decent fundraising success, and as two establishment candidates, are likely to get the GOP nod, even after summer talk about outsider candidate success.

Whether a friendship-turned-rivalry will get voters to believe in one candidate more than the other, tensions between Bush and Rubio have only begun.