WFIR Election 2016LEESBURG, Va. (AP) _ The final-days sprint to Super Tuesday is erupting into a feud over a white supremacist as Donald Trump’s Republican rivals scramble to stop the billionaire businessman from becoming an “unstoppable” force in the 2016 presidential contest. Ted Cruz and Marco Rubio continued to hammer the GOP front-runner’s character and lack of policy specifics in a series of attacks while courting voters across the South. But it was Trump’s refusal to denounce an implicit endorsement from former Ku Klux Klan leader David Duke that dominated the narrative less than two days before Republican voters across 11 states head to the polls. The new focus comes as Trump’s rivals acknowledge that time is running out to prevent the former reality television host from becoming the Republican Party’s presumptive nominee.