FROM Anne Kornblut
Potomac Primary Primer This year's tight contests for party nominations have focused attention on states that have never mattered much in presidential elections. Barack Obama swept to four victories in this weekend's primaries and caucuses. Mike Huckabee beat John McCain in Kansas and Louisiana and got close enough in Washington to challenge the outcome. In tomorrow's so-called "Potomac Primaries" in Maryland , Virginia and the District of Columbia , the focus is mostly on the Democrats. Anne Kornblut reports for the Washington Post .