Sen. Tim Scott R-S.C. speaks during the Values Voter Summit, held by the Family Research Council Action, Friday, Oct. 11, 2013, in Washington. (AP Photo/Jose Luis Magana)

Like a modern day Ben Franklin, Sen. Tim Scott makes his most critical decisions by listing the pros and cons on a sheet of paper.

So in recent weeks, as the South Carolina Republican tried to decide who to endorse for the GOP presidential nomination, Scott pulled out his detailed notes on the contenders along with his yellow legal pads and blue pens, crafting the rationale for each of the potential nominees as well as their downsides.

On Tuesday, he endorsed Sen. Marco Rubio (R-Fla.) — a fellow 40-something when they were first elected in 2010; both minorities in the white confines of Republican caucuses. What seemed like a natural decision from the outside came through one of the more detailed, painstaking processes any senator uses for choosing which horse to back in presidential politics.

In an interview, Scott explained that, indeed,  he really only had one choice once he had done his due diligence.“When I put together a strong position on national defense and foreign policy, coupled with a compassionate attachment for people to alleviate poverty using conservative principles exclusively, Marco Rubio became the only candidate that I honestly believe can do both,” he said.

The endorsement served as another boost to Rubio’s campaign, which shot out of the Iowa caucuses with a better-than-expected finish in third, narrowly edged out by Donald Trump for second and not far behind Sen. Ted Cruz’s (R-Texas) winning slot. Rubio, who has tried to position himself as a next-generation leader, has also focused on winning endorsements from less tenured lawmakers, such as Sen. Cory Gardner (R-Colo.) and Rep. Trey Gowdy (R-S.C.), both of whom were also elected in the 2010 Republican tidal wave.

Scott said that he’s aware endorsements don’t always add up to actual votes from real voters — that transference is one of the most difficult acts in politics. He said that he will travel to New Hampshire in the coming days to be with Rubio in advance of Tuesday’s primary, where Cruz’s staunch conservatism isn’t expected to play as well and Rubio might have a chance for a strong second-place finish or to even leap into first ahead of Trump.

Scott’s real focus, however, will be in South Carolina, which is shaping up in its usually pivotal fashion. “We’ll find out in 18 days,” Scott said Tuesday, counting down to the Feb. 20 showdown in his home state.

Getting to that point, however, took more than six months of detailed deliberation, note taking and face-to-face interaction between a dozen candidates and arguably the most sought-after endorser in the U.S. Senate. Scott, now 50, is the only African-American Republican in the Senate, and his personal biography of going from a childhood in poverty in North Charleston to making it into the Senate is the stuff of Republican storybook legend.

[Read how the Ryan-Scott poverty summit brought the issue to the 2016 forefront.]

Moreover, his blessing carries more than just symbolic weight because South Carolina is third in line in the presidential nominating process, after Iowa and New Hampshire. Scott is surpassed in popularity only by Gov. Nikki Haley (R) among Palmetto State leaders. In the interview, he acknowledged a “fairly assertive courting process” by the Republican contenders to get his backing.

Scott could’ve easily avoided the pressure of choosing because he is up for reelection this year. Haley appointed Scott to his Senate seat in 2013, after Jim DeMint (R-S.C.) decided to quit midterm to the Heritage Foundation. He won the remainder of DeMint’s term outright in November 2014, but now must stand for election in November to win a full six-year term.

Rather than taking a pass on endorsing anyone, Scott instead decided to maximize his leverage. He put a premium on issues of fighting poverty and upward mobility that are not part of the normal Republican primary vocabulary. Beginning in late August, Scott hosted 12 different town halls with presidential candidates spread all across the state, including everyone from onetime front-runner Donald Trump to his South Carolina partner, Sen. Lindsey Graham, whose own presidential bid came to an end in December.

At each event, Scott said, he took detailed notes of how the candidates handled questions from his constituents on the biggest issues of the day, with a particular focus on national security and poverty.

“Yellow pads and blue ink, a lot of it,” he said, describing the process.

That wasn’t enough, and so in early January Scott hosted what was billed as a “poverty summit”, along with House Speaker Paul D. Ryan (R-Wis.), in Columbia, S.C.. Six GOP hopefuls showed up, but Trump and Cruz were off campaigning in Iowa.

As Scott moderated the event, that’s when he began to settle on Rubio who, like Scott, uses his up-from-bootstraps story to talk about his aspiration for America.

“I think it all culminated at my poverty summit,” he said, explaining that he wants a candidate for the “next American century” rather than someone talking about the past. “I think it’s incredibly important for us to have a candidate who can win by using conservative principles — and that means you have to be able to sell those conservative principles so you need an aspirational candidate.”

But he still wasn’t settled. So, in recent weeks, that meant breaking out the legal pads and blue pens, again, crossing the line down the middle, and drawing up the pluses and minuses for each candidate.

Finally, Tuesday, the decision arrived. Rubio’s name got circled.