A week of rapid-fire congressional special elections kicks off Tuesday with a primary in Massachusetts’ 5th District, followed by two more contests in the following days to fill vacant seats on Capitol Hill.

Both the Massachusetts contest and a special election primary in Louisiana’s 5th District on Saturday are taking place in safe Democratic and Republican seats respectively, leaving little chance for either party to flip a new seat into their column. Yet with crowded primary fields in both races, it’s not clear which candidates will emerge with the nominations.

There’s a third special election on Wednesday in New Jersey to fill the seat of the late Democratic Sen. Frank R. Lautenberg. Newark Mayor Cory Booker is favored to keep that seat in Democratic hands.

In Massachusetts, the candidate who garners the most votes in the five-candidate Democratic primary will be the next member of Congress from this heavily Democratic district in the Boston suburbs.

Many local operatives say the special primary is state Sen. Katherine Clark’s to lose. But she is trailed closely by state Sen. Karen Spilka and Middlesex County Sheriff Peter Koutoujian — both of whom have a shot in what local Democrats expect to be an extremely low turnout contest.

In Louisiana’s 5th District, quirky election laws make this crowded primary field even more unpredictable. The 14 candidates running from both sides of the aisle will all appear on the same primary ballot. If no candidate receives 50 percent, the race heads to a runoff between the top-two vote getters, regardless of party.

GOP state Sen. Neil Riser is widely expected to receive the most votes in the contest, which takes place Saturday.

If former Rep. Clyde Holloway, state Rep. Jay Morris or businessman Vance McAllister make it into the runoff, either of these three Republicans would make this a competitive race up until Nov. 16.

However, there’s a chance that Monroe Mayor Jamie Mayo, a Democrat, makes the runoff instead, if the Republicans in the race splinter the GOP vote. If Mayo makes the runoff, Riser would likely coast to victory in this strong GOP district.

In New Jersey, Booker has largely cruised through the special election process. Rather than whether he will win, the more salient question has been what kind of senator the nationally known mayor would be. Entertainment industry friends helped him raise nearly $3 million just in the past two months.

After a dominating performance in the Democratic primary, Booker has continued to hold double-digit leads — including a 14-point margin in a Quinnipiac University poll released Tuesday — over conservative activist Steve Lonegan. A Republican hasn’t been elected to the Senate from the Garden State since 1972.