(Combined Sources) Democratic voters in four of the state’s nine congressional districts will have a chance to pick a new nominee to represent their party during Tuesday’s Massachusetts primary. In three districts, challengers from within the party are hoping to bump incumbent Democratic House members out of the running. And in the state’s 4th Congressional District, voters will choose from seven Democratic candidates hoping to fill the seat left vacant by Rep. Joe Kennedy III’s decision to challenge incumbent Sen. Edward Markey in the Democratic Senate primary. Winners in two of the four primaries will face Republican candidates in November.