Republican National Committee chairman Reince Priebus has been increasingly alarmed by the erratic behavior of the party's presidential nominee, Donald Trump, and has communicated his concerns to Trump campaign leadership in a series of tense conversations over the past two weeks, according to sources familiar with the back and forth.

The New York Times reported Tuesday that RNC Chairman Reince Priebus is "furious" that Donald Trump is refusing to endorse Paul Ryan, a close friend and longtime political ally. The Times report is accurate, but Priebus was frustrated with Trump and his campaign long before Trump's cheeky comments balking on supporting Ryan. The RNC chairman has expressed his frustration repeatedly in recent days on a variety of issues including Trump's reckless comments about potential Russian influence in the U.S. elections and his Trump's aggressive handling of the parents of Army captain Humayun Khan.

At times Priebus, usually a disciplined party-line spokesman, has voiced his difference with the GOP nominee in public. During a July 29 interview on Fox News's Hannity Priebus contradicted Trump on the DNC email hack and the possibility that a foreign power has Hillary Clinton's emails. Trump, for instance, greeted the news of a possible Clinton hack with glee and said that he hopes the Russians, or the responsible party, would make those emails public. Trump said American journalists would treat the Russians very well if they were to release them. Priebus, on the other hand, said: "We don't wish this on anyone."

Two days later, on July 31, Priebus told THE WEEKLY STANDARD: "As I've said many times last week, God forbid if any foreign government finds those emails—we don't want that to happen."

Priebus has also challenged Trump on his treatment of Khizr and Ghazala Khan, the parents of U.S. Army captain Humayun Khan, killed in Iraq in 2004. Even as Trump was attacking them, Priebus told Wolf Blitzer of CNN and Greta Van Susteren of Fox News on Monday that Khan's parents should be "off limits" to such attacks. And without being asked about it, Priebus took a subtle shot at Trump's claims that he, too, had sacrificed much for his country. "I think the Gold Star families should be off limits. I mean, I think that the Gold Star families, like I said before, whatever sacrifices I think that I have made or you or anyone watching this have made, they are crumbs on the floor compared to these Gold Star families. So I think the point is that we cherish and honor these families that are grieving and everything else. So, that is my position on it and I have made that clear to Republicans throughout the country that have reached out to me."

In his interview with Van Susteren, the strongest praise Priebus would offer for Trump was that he was the better of two options. When Van Susteren asked Priebus whether Trump's mishandling of the Khan controversy was "fatal," Priebus initially said he didn't think it was. But moments later, he seemed to leave open the possibility that it might be, saying "we'll have to wait and see."

Priebus hasn't split from Trump, and there's no indication that such a public break is coming. But those familiar with his thinking say his concern his real and predates Trump's unwillingness to support Ryan.

There's no doubt Priebus is reflecting the anxieties of Republicans across the country in his comments about Trump. Priebus told Van Susteren that he'd received texts and emails from Republicans across the country expressing concern about Trump's continued campaign against the Khans. But sources tell TWS that Priebus, whose job as party chairman it is to keep the party together and promote its candidates, has been saying these things—in private and in public—not just in order to amplify the concerns of party members but because he shares them.