All 200 seats in the Massachusetts Legislature are up for re-election this fall, but nearly two-thirds of sitting members are on a glide path toward another term with minimal opposition.

A total of 125 incumbent lawmakers, including members in both parties, were the only major-party candidates in their districts to file nomination papers with Secretary of State William Galvin by Tuesday's deadline, according to data compiled by Galvin's office and analyzed by the News Service.

They could still receive challenges from write-in campaigns. But the ballots are largely set, and as it stands now, none of those 125 legislators -- representing 62.5 percent of the General Court -- will face a declared Republican or Democratic opponent in either the Sept. 1 primary election or Nov. 3 general election.

The landscape means voters all over Massachusetts will have no choices to make in legislative races at a time when the state is struggling with major public health, economic, budgetary, and racial justice crises.

Fifteen legislative seats will be open and up for grabs this election season, 14 of which are currently represented by House lawmakers who opted not to seek another two-year term. One more seat will remain vacant until voters choose a successor to former Rep. John Velis, who won a special election to the Senate.

The remaining 60 races -- 48 in the House and 12 in the Senate -- will feature competition in either the primary or general election or both, including five seats that have been filled through special elections after lawmakers quit mid-term.

Seventeen Democratic members of the House face primary challengers, including Second Assistant House Majority Leader Paul Donato of Medford, Housing Committee Co-chair Kevin Honan of Allston, Election Laws Committee Co-chair John Lawn of Watertown, and Revenue Committee Co-chair Mark Cusack of Braintree.

Lowell Rep. David Nangle, who stepped down from his leadership and committee posts in February after he pleaded not guilty to more than two dozen federal fraud charges, filed nomination papers to seek re-election. He faces two primary challengers, Lisa Arnold and Vanna Howard.

Only one Republican in the House, Rep. Nicolas Boldyga of Southwick, will have a declared primary race, against Agawam's Dino Mercadante.

In the Senate, five of the 36 Democrats face primaries: Financial Services Committee Chair James Welch of West Springfield; Patricia Jehlen of Somerville, who co-chairs both the Elder Affairs Committee and the Labor and Workforce Development Committee; Veterans and Federal Affairs Committee Co-chair Walter Timilty of Milton; and Export Development Committee Co-chair Nick Collins of South Boston.

The fifth senator with a Democratic primary challenger, Brockton's Michael Brady, had been the chamber's top member on the Public Service Committee until the Senate stripped his position in November following his drunk driving arrest.

Only one state legislative primary drew four candidates from the same party, for the 12th Suffolk House seat currently held by outgoing Rep. Daniel Cullinane.

The 4th Congressional District race, however, is far more crowded: a total of 11 candidates are on the ballot to succeed Congressman Joe Kennedy III, who himself is in the midst of a heated primary race against U.S. Sen. Ed Markey.

Nine Democrats made the Sept. 1 primary ballot for the congressional seat: Jake Auchincloss and Becky Grossman of Newton; Dave Cavell, Alan Khazei, Ihssane Leckey, Natalia Linos, Jesse Mermell and Ben Sigel of Brookline; and Chris Zannetos of Wellesley.

Whoever emerges on top of that race will face either Julie Hall of Attleboro or David Rosa of Dighton, both Republicans.

In the U.S. Senate race, Kennedy and Markey are joined by Republicans Kevin O'Connor and Shiva Ayyadurai.

Three other congressional seats will involve primary elections: Holyoke Mayor Alex Morse is challenging Rep. Richard Neal, Robbie Goldstein will vie for Rep. Stephen Lynch's seat, and Rep. Seth Moulton faces opposition from both Jamie Belsito and Angus McQuilken.

The winner of that primary for the 6th Congressional District will face John Paul Moran in the general election. Reps. James McGovern, Katherine Clark and Bill Keating face Republican opponents Tracy Lyn Lovvorn, Caroline Colarusso and Helen Brady, respectively.

Congresswomen Lori Trahan -- who emerged narrowly victorious in a 10-way Democratic primary two years ago following a recount -- and Ayanna Pressley, the newest members of the delegation, have no major primary or general-election opponents on the ballot.

Ballot listings can still be withdrawn or challenged by Friday. For federal races, unenrolled candidates have until Aug. 25 to file papers to make the general election ballot.

Democrats hold supermajorities in both Massachusetts legislative chambers, currently outnumbering Republicans 125-31 in the House -- plus two more Democrats who won Tuesday special elections but have not yet been sworn in -- and 36-4 in the Senate.

They already added to their significant majority mid-session by winning all five special elections, three of which flipped Republican-held seats, and will look to ride November's presidential election to build on their numbers.

The 2020 elections appear likely to be conducted with a far greater portion of mail-in ballots than ever before as a precaution against the COVID-19 pandemic, particularly as experts warn that a second surge could hit this fall.

The House this week is advancing legislation that would require Galvin to send every registered voter an application for a mail-in primary and general election ballot.