On February 3, it became known that Rick Santorum is about to drop out of the Republican presidential race. See this story. Santorum had qualified for the Republican presidential primary in every state in which the deadline has passed. That is also true of Rand Paul, who also dropped out on February 3.
On February 3, the Kentucky Libertarian and Constitution Parties filed this brief in Libertarian Party of Kentucky v Grimes, e.d., 3:15cv-86. This is the case filed on December 4, 2015, that challenges the Kentucky definition of “political party.” In Kentucky, a group can become a qualified party only by polling 2% for President. There is no other means for a group to become qualified. Kentucky and Washington are the only two states for which this is true.
On February 2, the Georgia Green and Constitution Parties filed this reply brief in Green Party of Georgia v Kemp, n.d., 1:12cv-1822. The issue is the Georgia law that requires independent presidential candidates, and newly-qualifying parties, to submit over 50,000 valid signatures to get on the ballot.
The Ninth Circuit has chosen May, 2016, for oral arguments in two important election law cases: (1) Arizona Green Party v Reagan, 14-15976, over Arizona’s February petition deadline for newly-qualifying parties; (2) Democratic Party of Hawaii v Nago, 13-17545, over the Democratic Party’s request for a closed primary for itself.
Fred Barbash has this analysis in the Washington Post of whether courts can entertain challenges to ballot access for possibly ineligible presidential candidates. He finds that such a challenge cannot work in federal courts, but might work in state courts. But the only surefire way to get into court would be for an elections administrator to bar the candidate first, and then of course the candidate could sue in either state or federal court.