Boston ? Nearly one year to the day after President Barack Obama was sworn into office as an agent of change, Massachusetts Senate candidates battled to the wire Monday in an election that threatened his agenda and reflected voters’ frustration with the status quo.

Democrat Martha Coakley and Republican Scott Brown scoured the state for votes on the eve of the special election to succeed the late Edward M. Kennedy, with the Democrats’ 60-vote Senate supermajority at stake.

From a distance, the president made one last appeal in a TV ad for Coakley.

Obama needs Coakley, the state’s attorney general, to win to deny Republicans the ability to block his initiatives — specifically the near-complete health care plan — with a filibuster-sustaining 41st Republican vote. A Coakley loss also would be an embarrassment, particularly because Obama has put so much political capital on the line.