Two Massachusetts state senators, Katherine Clark of Melrose and Will Brownsberger of Belmont, filed to run in Massachusetts' 5th district.

They join state Rep. Carl Sciortino in expressing interest in the seat.

The growing list of potential contenders for the seat reflects the prevailing opinion in Massachusetts that Markey has a relatively easy path to the nomination, and ultimately, election to the seat vacated by Secretary of State John KerryJohn Forbes KerryKerry: Trump's rhetoric gave North Korea a reason to say 'Hey, we need a bomb' Russian hackers targeted top US generals and statesmen: report Trump officials to offer clarity on UN relief funding next week MORE.

Since former Sen. Scott Brown (R-Mass.) announced he would not run for the seat, Republicans have been unable to recruit a strong candidate, and few Democrats or Republicans in the state expect the eventual Republican nominee to come out on top.

And though Markey faces a primary challenge from Rep. Stephen Lynch, he has a large financial advantage on Lynch and the backing of a number of big Democratic names in Massachusetts and Washington.

However, a recent poll showed Lynch slightly closing Markey's substantial lead. Markey still holds a double-digit lead on Lynch, but that lead diminished from 33 percentage points in January to 15 points in February.

No potential contenders have yet announced interest in Lynch's seat.