Newt Gingrich, In Chicago, Endorses Donald Trump

CHICAGO (CBS) -- Former presidential candidate and House Speaker Newt Gingrich endorsed Donald Trump on Thursday, and did not rule out joining Trump on the ticket.

"Why would you want to say no to the circus?" Gingrich said on the possibility of being Trump's running-mate. "I love the circus."

"I think any citizen has the obligation to listen to potential president of the United States."

Trump, while still about 100 delegates short of securing the nomination, is the presumptive GOP presidential candidate, after dispatching his final rivals earlier this month.

According to Bloomberg News, Trump has discussed selecting Gingrich. So on Thursday in Chicago--he was attending a forum--Gingrich was pressed to make a commitment, yes or no.

"As much as I would like to please you, I will not give you a yes or no," he said.

Gingrich, who ran for president in 2012, says he has been giving Trump general campaign advice and helping with strategy since January 2015.

He was also a firebrand in the Republican Party in the 1990s leading the GOP takeover of the U.S. House during the Clinton administration.

Gingrich acknowledged that Trump still has a lot to learn about politics.

He said he didn't endorse Trump earlier because former Trump rival John Kasich is a friend and that he respected the way Ted Cruz ran his campaign.