The Lindsey Graham record: A lot like John McCain, who also ran for president

South Carolina Sen. Lindsey Graham, right, with Arizona Sen. John McCain during McCain’s 2008 presidential campaign. (Corey Lowenstein/Raleigh News & Observer/MCT)

On Monday, Republican Lindsey Graham of South Carolina will become the fifth sitting senator to formally announce a presidential bid, but his biggest challenge to prove he’s a viable candidate likely won’t come directly from the crowded field of colleagues he’s currently running against. It will be from the one senator who already has waged (and lost) multiple bids for the White House: John McCain of Arizona.

For those who follow congressional politics, Graham and McCain have been inseparable — and practically indistinguishable — from each other for more than a decade, since Graham arrived to the Senate in 2003. Graham is often spotted just feet from the Senate floor, barking into a flip phone to a staffer about coordinating press strategy with McCain, meaning that “Statement by Senators John McCain and Lindsey Graham on [foreign policy issue X]” is a frequent refrain in reporters’ mailboxes. A search of McCain’s Senate website, for example , found 239 press releases mentioning “Lindsey Graham” since 2005, many of which are from the past two years.

Graham and McCain also make up the core two-thirds of a group known colloquially in Washington as the “Three Amigos,” which basically is a small nucleus of senators who have consistently advocated for more U.S. military intervention in the Middle East and have been searching for a permanent third “amigo” since “friend” Joe Lieberman, I-Conn., left the Senate in 2013. A Graham bid now completes an unofficial fraternity pledging ritual for the original group’s triumvirate: a presidential run.

With a 2016 Graham campaign, four of the last five presidential elections have featured an “amigo” vying for a place at the top of the ticket (Lieberman, 2004; McCain, 2000, 2008). But there’s no requirement for success in this political hazing process. Only once has a major party selected an amigo as its nominee — McCain in 2008 — and America has never elected one as president.

The “Three Amigos” — from left, Sens. McCain, Lieberman and Graham. (Brian Baer/Sacramento Bee/MCT via Getty)

The Iraq War, and McCain’s unwavering support of it, hurt him with a war-weary electorate in 2008. Graham, along with former Sen. Rick Santorum of Pennsylvania , will be the only Republicans in the 2016 primary field who actually voted for the Iraq War. (Democratic frontrunner Hillary Clinton also voted for the war.)