But the new pact goes further than Brown and Warren by restricting direct mail from outside groups — something left out of last cycle’s pledge — as well as TV, radio and online advertising.
It is unclear if Republican candidates in the race will sign on to the pledge in the general election, where outside spending will have its greatest impact.
Gabriel Gomez, a local businessman and former Navy SEAL, told the Boston Globe he had not made a decision on the pledge. He entered the race earlier this week.
The pact, dubbed the People’s Pledge, didn’t catch on in other Senate races last year, though a number of Democratic candidates did propose similar ideas. The success in Massachusetts seemed to hinge on Brown, a centrist Republican who supports campaign finance reform.
Brown and Warren’s pledge last year held up for the most part. In one of the most expensive Senate races in the country, outside spending was only about one tenth of what the two campaigns spent. Outside spending totaled about $8 million compared to $77 million spent by Brown and Warren.