Republican Sen. Lindsey Graham plans to announce his presidential campaign on June 1, GOP sources tell Fox News. Graham, a three-term senator from South Carolina, is known as a foreign policy hawk in Congress. Though he is considered a long shot -- and ranks near the bottom in recent polls of declared and potential Republican presidential candidates -- Graham could help drive the debate on national security among a GOP field that includes candidates who sharply question policies ranging from drone strikes to NSA surveillance.While it's true that Graham's views on national security are more palatable to the conservative base than (say) Rand Paul's, there are areas that may not be reconcilable. Graham is trying to establish himself not as the squishy "RINO" (Republican in Name Only) but as the "realist" in the field who will work in bipartisan fashion to accomplish his agenda. It seems reasonable, in that case, to recall some of his bipartisan efforts in recent years: Remember the "Year of Immigration Reform"? That was 2013, in case you missed it. The Gang of Eight is often evoked in discussion of Marco Rubio's amnesty flip-flop, but it's worth remembering that Rubio was not the only Republican member. Lindsey Graham was right there, effectively leading the GOP side: "We're going to be aggressive in marketing the bill. This is an all hands on deck approach."