Sen. Rand Paul has insisted he is too busy to attend the Republican National Convention, raising concerns over his refusal to endorse Donald Trump’s presidential campaign.

According to a report from Axios, Paul has confirmed he will not be attending the convention in Milwaukee this month.

“I’m busy,” he said when asked for an explanation as to why he wouldn’t be there.

Other Senators not attending the event include RINOs Mitt Romney of Utah, Susan Collins of Maine and Lisa Murkowski of Alaska, all of whom have confirmed they are not voting for the former president.

Paul’s refusal to attend the convention is all the more suspicious given his refusal to endorse Donald Trump over Joe Biden or his potential replacement.

Even Mitch McConnell, Paul’s fellow senator from Kentucky and a widely unpopular figure among the grassroots, has endorsed Donald Trump and will speak at the convention in support of his campaign.

Axios suggests that his refusal may be linked to a growing rift between Paul and Trump, amid reports that he was not incredibly happy with the levels of spending under the previous administration.

This reportedly included a “heated exchange with top Trump ally Russell Vought during a recent closed-door meeting,” where Paul argued he had “no credibility” on the issue.

He is also said to have a close relationship with Robert F. Kennedy Jr., who is running as an independent candidate on a left-wing, anti-establishment platform. However, it is unclear whether he would consider supporting his campaign.

There is, of course, a long time between now and November where one can expect Paul to come to his senses. Back in 2016, Trump’s main primary opponent Ted Cruz withheld his endorsement until September, although the two men eventually became close allies over the course of his administration.