Lindsey Graham already has his first endorsement for the presidency.

"He's my man," says Republican Sen. John McCain of Airzona, who won his party's endorsement in 2008 and knows his way around Iowa and New Hampshire. "He's a dark horse. Keep an eye on him."

Graham's formal launch Thursday of a political committee "Security Through Strength" left some on Capitol Hill scratching their heads. A few of his colleagues chuckled when asked in the marbled hallways what they thought of the defense hawk embarking on a serious presidential campaign.

Graham, who is known as a hardworking legislator, but not a senator with gravitas, is testing the waters at a time when the 2016 field is already packed with potential. The 2016 GOP primary could have a host of past and present GOP governors, from Scott Walker to Mitt Romney to Jeb Bush to Chris Christie. And many of Graham's colleagues, including Sens. Marco Rubio, R-Fla., Rand Paul, R-Ky., and Ted Cruz, R-Texas, have been laying the groundwork for their own campaigns for months.

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The Senate's No. 2 Republican, Texas's John Cornyn, said he'd be curious to see a list of Graham's supporters.

Sen. Dean Heller, R-Nev., worries about the consequences of too many Republicans seeking the nomination.

"The saying around here is that every congressman thinks he ought to be a senator and every senator thinks he ought to be president of the United States," Heller said, while noting that Graham has strong qualifications. "I am not one who thinks the more the merrier, because all we do is end up beating each other up. You hear very little criticism of Democrats of Sen. Clinton, and we are just pushing and shoving and beating each other up right now, and I hate to see that. I think it really weakens our hand."

Cruz, however, called Graham a "good man" with "deep passions" and welcomed him to enter the crowded race.

Graham's positions on Iran, Syria, and Iraq could push fellow contenders further to the right on foreign policy.

"I think it is entirely likely that we will see a crowded field, and that is a healthy thing," Cruz said. "I fully expect for the next year or more we will have a vigorous debate about the right direction for the Republican Party and the right direction for the country."

His colleagues say Graham does offer a foreign policy aptitude unparalleled in the 2016 fray. While Sens. Rubio, Paul, and Cruz have tried to quickly prove their international bonafides with policy speeches and CODELs, Graham's been at the center of the debate for more than a decade in the Senate.

"Who else is better on foreign policy than Lindsey Graham?" asks fellow Republican Sen. Tim Scott of South Carolina.

Sen. James Risch, R-Idaho, echoes that Graham "knows foreign policy about as well as anybody."

Some see Graham's entrance less as a serious bid and more as an effort to change the dynamics of the Republican primary. Graham's positions on Iran, Syria, and Iraq could push fellow contenders further to the right on foreign policy. Graham also could be a catalyst for the Republican Party to reach out to more minority voters. A key sponsor of the Senate's comprehensive immigration bill in the last Congress, Graham could be yet another person on the debate stage in the 2016 election who is on record supporting a path to citizenship for some of the immigrants who reside in the country illegally.

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That position could cost him in early states like Iowa and South Carolina, but it could also neutralize the issue for other contenders in the race who have held that position, such as Rubio and Bush. Ultimately, some senators say, Graham could help the Republican Party make strides with some Latino voters who have felt unwelcome in the GOP.

"He's one of the candidates that will appeal to a lot of different constituencies," Scott says. "He will bring a very unique perspective that draws conservatives and liberals together."

Graham has been telling colleagues for weeks that he intends to run for president. McCain, Graham's longtime Capitol Hill ally, said that reaction to Graham isn't all that different to what people said about him in 1999 when he first began exploring a run for the White House.

"When I announced in 1999, they laughed," McCain said. "I have no illusions about how it's an uphill battle. He has people who have lots of money and all that, but I certainly would never underestimate him and I have great confidence that he will be very competitive."

McCain says when it comes to Graham competing against all the others jockeying to be the GOP nominee, "in debates, he'll shred 'em."