(CNN) New Jersey Gov. Chris Christie — a former Donald Trump rival turned top defender — is being vetted as a possible running mate for the presumptive Republican nominee, a source confirmed to CNN on Thursday.

Christie has received the official paperwork for the vetting process, according to a source with knowledge of the process.

Trump has said he intends to announce his vice presidential nominee at the Republican National Convention in July in Cleveland.

The New York Times was first to report Christie’s vetting.

Though Christie ran against Trump in the GOP primary, the two have been long-time friends and Christie quickly endorsed Trump and became a reliable presence at his events after dropping out of the race.

The New Jersey governor has been one of Trump’s highest-profile surrogates, continually defending him against critics

When Trump was getting chastised by others in the GOP for his criticism of a federal judge over seeing a Trump University lawsuit, Christie said the billionaire was perfectly justified.

“In the end there are always going to be conflicts regarding civil lawsuits. People are always going to express their opinions. Those are Donald’s opinions, and he has a right to express them,” he said. “I can guarantee you that, you know, people who are going to vote today in (New Jersey) and people who are going to vote in November are not going to make their decision based upon this kerfuffle.”

He added: “I’ve known him for 14 years and Donald Trump is not a racist.”

Christie, a former chief of the Republican Governors Association, has been one of the few so-called establishment GOP politicians to rally to Trump’s side, one with a powerful fundraising network and political connections.

He has been the focus of VP speculation for some time, leaving the possibility open when asked by reporters.

A May Quinnipiac poll found that 72% of New Jersey voters and 64% of Republican New Jersey voters thought Trump should pick someone else for vice president.