People say 'blah' to say how boring democrats are. Sometimes, blah is said numerous times in a row to signify monotony.
ex. "Mexican bloodlines are much more genetically similar to Native Americans than any other ethnicity. Therefore, if anyone should be considered immigrants, it is us Americans, who migrated here from europe", translates into "Blah blah blah water under the bridge blah blah blah blah."