A constitutional amendment that could open the door to betting on historic horse races is facing a filibuster in the Nebraska Legislature. Sen. Scott Lautenbaugh of Omaha presented the measure Wednesday in legislative floor debate. Lautenbaugh is proposing a 2014 general-election ballot measure in which voters could give lawmakers the authority to allow betting on previously run horse races. The amendment was introduced along with another bill by Lautenbaugh that would allow betting on the races within a licensed racetrack area. Opponents say the measure is an effort to expand gambling in Nebraska. Lawmakers who oppose the measures have promised to delay the vote for as long as they can.