Sen. Mark Warner is less outspoken than some of his fellow junior Democrats, but he’s beginning to be seen as a powerful player in Congress.

The freshman Democrat from Virginia has never been known for flamboyance. Political reporters repeatedly knocked him during the early stages of the 2008 campaign for being boring.

But when he joined the Senate last year, Warner signaled he wanted to delve deep into the legislative process, hiring Luke Albee and Jonathan Davidson, two staffers with more than 30 years of Senate experience between them, as his senior aides.

And he’s given $87,500 from his leadership political action committee (PAC) to colleagues and Democratic candidates as well as $5,000 to the Nevada Democratic Party and $15,000 to the Democratic Senatorial Campaign Committee over the past 15 months. Warner, however, is tightlipped about this work.

“I’m happy to help my colleagues,” he said.

The senator also teamed up with Sen. Bob Corker (R-Tenn.) to tackle a major piece of financial regulatory reform: the problem of financial institutions becoming too big to fail.

In recent weeks he has reached out to Sen. Lindsey Graham (R-S.C.) on legislation to provide tax incentives for homes and offices that become more energy-efficient.

Graham said he had “a couple” of lunches and dinners with Warner and other senators in recent months and Warner suggested working together during one of those meals.

“He’s an easy guy to work with,” said Graham. “He seems willing to engage Republicans.”

John Podesta, president of the Center for American Progress, said Warner “is one of the few people that can still have a civil conversation with people across the aisle.”

Even after bipartisan negotiations on financial regulatory reform collapsed, Corker praised Warner as “the best partner anybody could possibly imagine.”

Warner’s rumored presidential ambitions, prodigious giving as a freshman and feverish activity have raised speculation among Senate insiders that he may aspire to a future in the Democratic leadership.

One senior Democratic aide said that a centrist could emerge as a dark horse in a potential leadership race between Senate Democratic Whip Dick Durbin (Ill.) and Senate Democratic Vice Chairman Charles Schumer (N.Y.) if Senate Majority Leader Harry Reid (D-Nev.) loses reelection. The aide speculated Warner could be a promising candidate, although he has the disadvantage of being a freshman.

Warner, in a brief hallway interview, dismissed that possibility as “baloney.”

But Warner took a more partisan stance Tuesday when he organized a Senate floor protest of GOP obstruction of President Barack Obama’s nominees.

Thirteen lawmakers made it to the floor to highlight what they called Republican abuse of Senate procedures.

In a large group of talented and energetic sophomore and freshman senators, such as Sheldon Whitehouse (D-R.I.), Sherrod Brown (D-Ohio) and Al Franken (D-Minn.), Warner cringes at the thought of coming off as a show horse instead of a workhorse.

Behind the scenes, he has worked to unify junior Democratic senators.

Warner helped put together a recent meeting between the Democratic classes of 2006 and 2008 to voice frustration over Republican use of the filibuster. That led to a meeting last week with Reid at which the majority leader pledged to pursue reform of the filibuster rule.

The Democratic freshman class — which totals 12 members — began meeting regularly at the start of the 111th Congress. Warner suggested the group take advantage of its influence as a large bloc of the conference by inviting guests to join it for briefings and discussions.

So far the group has met with Federal Reserve Chairman Ben Bernanke, National Security Adviser Jim Jones, Treasury Secretary Tim Geithner and Health and Human Services Secretary Kathleen Sebelius and had lunch with White House Chief of Staff Rahm Emanuel.

The regular policy discussions have helped forge a sense of identity and teamwork. And as the freshmen have learned the intricate workings of the chamber, they have sought to have a bigger impact.

Warner’s bustling activity has received little attention because he has preferred not to discuss with reporters his private interactions with colleagues.

But his role emerged during interviews with freshman and sophomore Democrats last week.

Senate Democratic leaders view Warner as one of the more promising new members of the conference and have given him challenging assignments.

Reid put him in charge of Senate Democratic outreach to the business community, a constituency that has had a rocky relationship with the party over the years.

But Warner, who co-founded the company that became Nextel and earned millions in the telecommunications industry, has won rave reviews from business leaders.

John Castellani, president of the Business Roundtable, an association of corporate CEOs, said Warner helped to get his group more comfortable with the Senate healthcare bill. Warner was one of the leaders of a group of freshman Democrats who offered a package of amendments to contain costs, encourage innovation and promote accountability across the healthcare system.

The freshmen won the early support of Maine Republican Sens. Olympia Snowe and Susan Collins and won adoption of the package, a rare and significant bipartisan victory.

“They moved us from being neutral and skeptical [about the bill] to positive enough that we encouraged the Senate to move forward,” Castellani said.

Castellani said he could not even recall who handled business outreach to Democrats before Warner. “He’s one of those few members of the Senate who understands the business side and gets how the business has to operate,” said Castellani.