Coakley vs. Brown: President Obama's Agenda Hangs in Balance

WASHINGTON, Jan. 17, 2010— -- What happens Tuesday in Massachusetts could affect the entire nation, and President Obama's whole future domestic agenda.

The state's voters will go to the polls Tuesday to choose between Democratic state Attorney General Martha Coakley and Republican state Sen. Scott Brown in a surprisingly close special election to fill the seat held by the late-Sen. Ted Kennedy for 46 years.

If Brown wins, he would break the filibuster-proof 60-seat majority Democrats currently hold in the Senate, a majority that is deemed crucial for passage of health care reform and other top White House initiatives.

In a sign of how high the stakes are, Obama flew to Boston today to appeal to Massachusetts voters in person. To a cheering and elated crowd, Obama brought back some of his fiery campaign rhetoric.

"Fired up?" he asked the crowd, who seemed energized as soon as he took the stage at Northeastern University.

The president tied Brown's agenda with "Washington Republicans" who are against financial reform, clean energy and health care reform.

"When the chips are down, when the tough votes come, on all the fights that matter to middle class folks of the Commonwealth, who is going to be on your side?" he asked.

If elected, Brown would be the 41st Republican senator, enough to block the President's health care bill from final passage. Brown, 50, has vowed to vote against it.

"As the 41st senator I can at least allow them to, you know, maybe look at things a little differently," Brown told ABC News in an interview.

Political analysts say that if Brown wins, the Democrats' health care reform initiative is in serious danger.