ROXBURY CROSSING, MASS. -- President Obama joined a parade of top Democrats rallying support for the Senate campaign of Rep. Ed Markey of Massachusetts, who’s in a surprisingly tough contest to win the seat vacated by Secretary of State John Kerry.

Frightened of a repeat of what happened in 2010 in the race to replace the late Sen. Edward Kennedy – when Republican Scott Brown won an unexpected victory over Democratic state attorney general Martha Coakley – Democrats are taking no chances this time.