Wearing his trademark sweater vest and bringing one as a gift for his host while appearing as a guest on "The Tonight Show with Jay Leno," Rick Santorum explained why he endorsed Mitt Romney in a lukewarm email that was sent to his supporters.

"You endorsed Mitt Romney last night in an email," Leno said to Santorum. "I thought you would be in bed at 11:00 at night."

Santorum laughed and said, "We have seven kids so we don't sleep."

"Now why in the middle of the night?" asked Leno. "It seems kind of tepid, doesn't it?"

Santorum, who seemed relaxed and wore a mischievous grin at times during the interview, said it just took him time to embrace his former rival, and mentioned the meeting the two had in Pittsburgh on Friday.

"I think we just needed some time," Santorum told Leno. "It was a rough-and-tumble campaign. I can't say it would have been an easy thing the next day to turn around and say, 'Let's just go forward.' It was tough and so I wanted an opportunity to, sort of, think about it a little bit and [let the] family think about it."

He added that he "has some concerns" he wanted to discuss with Romney before formally endorsing him.

"I voiced some of the things that I thought were important for us if we are going to be successful in this general election that he would take the cudgel and run with it," Santorum said, before explaining why the email came in after 11 p.m. at night.

"We decided to put it out late at night so it would be, sort of, the first thing people would see in the morning," Santorum said.

Santorum's email to supporters was also quite lengthy, and Leno pointed out Santorum didn't actually explicitly mention he was endorsing Romney until the 13 th paragraph of a 16 paragraph email, saying it was "kind of buried."

Santorum explained that it was a letter to his supporters telling them why they should "rally around Mitt Romney" and he explained that he "laid out, sort of, the case and just said, you know, 'here's sort of what we went through.'"

Leno brought up Santorum calling Romney the "worst Republican in the country to put up against Barack Obama" on the campaign trail. Santorum answered that he was talking about the issue of "Obamacare" and he acknowledged that "unfortunately" the presumptive GOP nominee was the "Romneycare author," which was the "predecessor of Obamacare," but he trusts that Romney will "work with the Republican Congress to repeal it."

Leno said he was a native of Massachusetts and people seemed to like "Romneycare" in his home state. He went back and forth with Santorum about why if the programs are state health care plans as opposed to federal why they are still not a good idea.

"Can you imagine what 'The Tonight Show' would look like if the government ran 'The Tonight Show'?" Santorum asked Leno.

Leno quipped, "I see what it looks like with NBC running it!"

Santorum's warmest words for his rival came at the very end of the interview when Leno shook his hand and asked if he was going to give it another go and run in 2016.

The former candidate did not hesitate: "We are going to have a Republican president," referring to Romney.

"The Tonight Show" host also asked Santorum about the campaign's focus on contraception. The former Pennsylvania senator stressed "his religious beliefs" ban the use of birth control, but he does not believe it should be mandated.

"My religious belief is [that] contraception is wrong, and, therefore, my wife and I don't believe in that," Santorum said. "But I would never impose that on anybody else. I've never voted to stop contraception. I just don't believe that - I think the whole act, and this goes from my Catholic faith, and we should be open to life … there are lot of things I believe. I don't believe in smoking, but I'm not - I wouldn't vote for any bans on smoking."

Leno interrupted and said he would be for a smoking ban.

"I wouldn't," Santorum said. "I don't believe that the government's role is to say everything we think is good for you or bad for you, the government has to have a law that says it's good or bad."

Leno didn't skip a beat: "So a gay couple smoking with a contraceptive would be the worst thing."

Santorum threw up his hands in mock horror and replied, "Oh, my gosh," said Santorum, laughing. "Heaven forbid."