(CNN) – Sen. Rand Paul, R-Kentucky, is so serious about running for president, he is actively taking all the steps "that someone in his position should be making," a GOP source familiar with Paul's activities told CNN.
His activities and travel plans indicate he wants to be a serious candidate with a real path to victory, the source said. He would be running to win-not to make a statement, an approach that his father, former Rep. Ron Paul, embraced in the most recent presidential election.
The first-term senator, who dominated national headlines this week with his nearly-13 hour filibuster, is staying in touch with grassroots activists who supported him and his father. Both Pauls are known for their libertarian leanings-though the younger Paul has notably struggled to woo some of his father's most ardent supporters.
According to the GOP source, Paul has a robust email list with more than two million addresses. He's been trying to build new relationships among grassroots supporters, by signing letters and sending emails for groups.
He's also been active in establishing relationships and building an informal finance committee. His team has been working to find donors with big pockets to supplement the small donor component of his and his father's political operation.
He plans to travel to South Carolina, which holds the first-in-the-nation primary, in the not too distant future, the source said. Paul made "soft promises" to people in other early voting states, including New Hampshire, Iowa and Nevada. The senator, however, doesn't think those trips are all that critical at this early stage, the source said.
In January, Paul also stoked speculation of a 2016 bid when he went to the Middle East and met with leaders in Jordan, Israel and the Palestinian leadership.
But how does the son differentiate himself from his father, who ran for president three times, on the national political stage?
"At the end of the day, Ron saw himself as a truth teller but he hated politics. He didn't want to think about how to message things. He wanted to travel around and speak truth and let chips fall where they may," the source said. "Rand wants to be honest and truthful and principled, but he is very conscious of his messaging and language. He wants to make a winning political argument."
Rand Paul is also trying to stake out his own claim in terms of foreign policy. While Ron is very much a non-interventionist, Rand is trying to forge a "third way" – comparing himself to George W. Bush circa 1999. He doesn't want to nation-build and he wants to be less bellicose and less aggressive than other Republicans, but still be aggressive and engaged in the world.
With the help of Senate Minority Leader and fellow Kentucky Sen. Mitch McConnell, Rand Paul was put on the foreign relations committee (over the objections of some more traditional Republicans). That position gives him more credible experience on foreign policy–a topic many struggle with on the campaign trail.