These days, Sen. Marco Rubio of Florida is reluctant to criticize President Donald Trump. But back in 2016 — when they were competing for the GOP presidential nomination — there was very bad blood between the two Republicans. And NBC News is reporting that according to a newly discovered batch of 2015 and 2016 e-mails, Trump ally Stephen Miller tried to plant anti-Rubio articles in Breitbart News during Trump’s campaign.

The leaked e-mails were given to the Southern Poverty Law Center (SPLC) by former Breitbart staff writer Katie McHugh. And those e-mails, according to Ben Collins and Anna Schecter of NBC News, “offer a window into just how closely Miller coordinated with Breitbart.”

Miller, now a policy adviser in the Trump Administration, worked on Trump’s campaign in 2015 and 2016. According to Collins and Schecter, the e-mails “show that Miller repeatedly sent McHugh editorial guidance.”

One of those Miller/McHugh e-mail exchanges is from December 2015, when McHugh agreed to cover an undocumented immigrant who was arrested for allegedly raping a child — and Miller wanted her to “work in” that Rubio favored legislation that would encourage undocumented immigrants to commit crimes.

“Can you work in a reminder that Rubio’s bill — which he was pushing for Obama — legalized alien sex offenders, ensuring more such rapes would occur?,” Miller wrote in an e-mail to McHugh.

In other e-mails to McHugh, NBC News reports, Miller described Rubio (who is Cuban-American) as “pathological” and “an extremist who wants unlimited immigration.”

McHugh told NBC News, “Stephen Miller is an extremist, and for some reason, he had this pathological determination to tank Rubio’s campaign.”

In 2015 and 2016, McHugh’s work for Breitbart News was notoriously racist — and she was fired in 2017 for being too racist even for Breitbart. But McHugh has since renounced the white nationalist views she once promoted.

E-mails leaked last week show Miller pointing McHugh in the direction of racist websites like American Renaissance and VDare and indicate that he considered them credible sources of information.

“Stephen Miller is a very intense and obsessive person,” McHugh told NBC News. “He’s one of those white nationalists who puts a veneer of intellectualism on things; so, he was able to get away with them.”