Democratic U.S. presidential hopeful and former U.S. Secretary of State Hillary Clinton waves to tourist while walking throught the U.S. Capitol rotunda, July 14, 2015. Clinton spent the day visiting with Congressional Democrats. Getty Images/Mark Wilson

WASHINGTON -- Hillary Clinton spent a news-filled day holding court on Capitol Hill, meeting with groups of Democratic lawmakers to talk policy and politics. Her visit, which fell the same day President Barack Obama announced a landmark nuclear deal with Iran, was aimed at shoring up support from lawmakers who can be crucial surrogates during the presidential campaign.

Nearly half of the Democrats in Congress have already endorsed Clinton’s 2016 bid. But winning over the rest of them -- or at least showing them you’re willing to sit down and hold conversations -- could reap benefits for Clinton down the road.

In 2008, Clinton expected that she would quickly earn the endorsements of many members of Congress. But many members instead opted to endorse Obama. Nearly the entire Senate endorsed Obama, and less than half the House Democrats got behind Clinton.

Democratic U.S. presidential hopeful and former U.S. Secretary of State Hillary Clinton (L) hugs House Minority Leader Rep. Nancy Pelosi as they speak to members of the media, July 14, 2015, on Capitol Hill in Washington, D.C. Clinton visited the Hill on Tuesday, and she had a meeting with the House Democratic caucus earlier in the morning. Getty Images/Alex Wong

Endorsements can be crucial in hard-fought primaries. The old adage -- people hate Congress but love their own member of Congress -- often holds true, giving representatives strong sway with undecided voters in crucial districts.

With Clinton so far ahead of her competitors, members of Congress must also consider staying on the good side of the likely nominee. Presidential campaigns can have a large impact on local, down-ballot races. Whether a presidential nominee spends money in a district or holds a campaign rally can affect the outcome of a congressional candidate’s race.

Even though Hillary Clinton once served in the Senate, her arrival in the Capitol drew many onlookers. Interns and staff crowded in hallways to catch a glimpse of her. A flock of reporters followed her around the building. (Taylor Swift was also in town for a couple of concerts, and she sparked even more excitement.)

Clinton began her morning with House Minority Leader Nancy Pelosi, who has yet to endorse in the Democratic primary but has heaped praise on the former secretary of state. She then met with all of the House Democrats -- a large group whose endorsements could help her along the way.

Democratic presidential candidate and former Secretary of State Hillary Clinton heads to a meeting with the Congressional Progressive Caucus at the U.S. Capitol July 14, 2015 in Washington, DC. Clinton had six different meetings on Capitol Hill with members of Congress, including the Senate Democrats. Getty Images/Chip Somodevilla

After the meeting, where attendees said she offered a "full-throated" endorsement of the Iran deal, Clinton delivered remarks to the press along with Pelosi. “All in all, I think we have to look at this seriously and evaluate it carefully, but I believe based on what I know now, this is an important step,” Clinton said of the Iran deal.

She met with several of the caucuses: the Congressional Black Caucus, the Congressional Hispanic Caucus, the Congressional Asian Pacific American Caucus and the Congressional Progressive Caucus. At the Hispanic caucus meeting, Clinton discussed the economy, immigration reform, healthcare and the wage gap in our country, according to one attendee.

She then visited the Senate Democrats' weekly luncheon -- where primary rival Sen. Bernie Sanders, D-Vt., was in attendance. By all accounts, the closed-door meeting with Sanders was pleasant and congenial.

There was time for at least one jab. House Speaker John Boehner, when asked about Clinton's visit to the Capitol, took the opportunity to bring up the House Benghazi Committee's continued investigation into the former secretary of state's use of a personal email account. "I wonder if she brought her emails with her," Boehner said.