Attorney General Maura Healey announce last Thursday that she will be a candidate for governor this year, and former Boston Mayor Marty Walsh has announced he won't join the race.

"If something's working, let's keep with it," Healey said outside an East Boston MBTA station. "And if it's not working, let's figure out what we need to do."

The announcement comes after Gov. Charlie Baker and Lt. Gov. Karen Polito said in November that they won't seek reelection for a third term.

There are three other declared candidates in the race: state Sen. Sonia Chang-Diaz and Harvard Professor Danielle Allen, both Democrats, as well as Republican former state Rep. Geoff Diehl, who lost a 2018 U.S. Senate race against Sen. Elizabeth Warren. With a $3.7 million war chest and high name recognition, many consider Healey the candidate to beat.