The Texas Democratic Party does not permit Democrats to run in its presidential primary unless they pledge to “fully support” the party’s eventual presidential nominee. Congressman Dennis Kucinich refused to sign that oath in 2008, so was kept off the Texas Democratic primary ballot. He had challenged the party in court but lost the case in both U.S. District Court and the 5th circuit. He has decided not to ask for U.S. Supreme Court review.
However, he will ask the Democratic National Committee to tell the Texas Democratic Party that it should drop the oath. No other state unit of a major party has a similar oath for candidates in its presidential primaries.