washington president barack obama maintain pressure senate approve supreme court nominee need republican u.s. senators seek re-election keep conservative voters happy primary elections come months work april 26 sept. 13 nine state incumbent republicans grip u.s. senate seat tenuous hold party primaries ahead nov. congressional presidential elections period republicans seem unlikely break senate majority leader mitch mcconnell hard-line stance hold confirmation hear vote obama nominee appellate judge merrick garland mcconnell insist obama successor elect november take office january fill vacancy leave february death justice antonin scalia republicans hop party candidate win presidency make appointment supreme court appointment require senate confirmation voice support hold garland hear primary season political experts say could enrage conservatives already upset prospect obama make third lifetime appointment nine-member court could give bench liberal tilt first time decades anger could bolster primary candidates challenge incumbent republicans right encourage new challengers come forward political science professor sheldon goldman university massachusetts amherst track supreme court nominations since 1960s say garland fight real obstacle get primaries danger stray mcconnell blockade illustrate kansas republican jerry moran last month back hear garland reverse course rumble right-wing challenge materialize moran aug. primary key battlegrounds senate republicans include wisconsin pennsylvania florida new hampshire new hampshire kelly ayotte view one vulnerable senate republican incumbents ayotte meet garland say want senate wait november elections act nomination arizona senator john mccain face least two opponents aug. 30 republican primary downplay political difficulties present garland nomination say home recent senate recess hear complaints constituents mccain say would ask would explain obama fellow democrats senate continue press republicans allow hear summer think circumstance republicans senate decide placate base important uphold constitutional institutional roles democracy way dangerous obama say chicago thursday democrats think mcconnell gambit give campaign issue elections dick durbin senate democrat say question obstruction unite state senate happen vacancy supreme court exhibit republican obstructionism senate primary-race pressure work obama 's court nominee