washington u.s. vice president joe biden praise democratic presidential candidate bernie sanders tap americans concern grow income inequality potentially give vermont senator boost gain rival hillary clinton weeks iowa caucus sanders argue authentic choice party nominee try undermine clinton double-digit lead national poll gain grind important early nominate state iowa new hampshire interview cnn monday night biden say sanders focus grow gap rich americans strike chord voters bernie speak yearn deep real credibility biden say absolute enormous concentration wealth small group people new class able show leave out say clinton campaign iowa tuesday focus income inequality long relatively new hillary talk biden say hillary focus things bernie one question bernie authenticity issue tuesday biden say criticism clinton former u.s. secretary state tell nbc today show focus rightly foreign policy income inequality long sanders mantra even income inequality serious today drumbeat biden say come good ideas bernie push envelope this biden interview come president barack obama final state union address tuesday night clinton large national lead poll struggle make solid gain iowa new hampshire hold outsized influence election process tuesday quinnipiac university poll show sanders climb 49 percent iowa percentage point lead clinton go feb. caucus widen lead new hampshire 14 point monmouth university poll say poll error margin 4.4 4.8 point respectively biden court democrats seek presidential nomination decline cite family obligations son beau biden die cancer last year within party concern remain whether clinton overcome lack enthusiasm among voters biden also tell cnn obama want influence presidential nominees november white house election especially gun control clinton increasingly criticize sanders past vote view favorably national rifle association biden say sanders make improvements position bernie sanders say second amendment say late second amendment say limit gun people criminals gun biden say people schizophrenic mental illnesses gun say that 2016 presidential race see reuters blog tales trail biden sanders 'struck chord voters race clinton