Democrat Scott Murphy scored a big endorsement Wednesday when President Barack Obama sent an e-mail to supporters asking them to back his candidacy in New York’s 20th District special election.

“Scott has the kind of experience and background we desperately need right now in Washington,” Obama wrote, urging his supporters to chip in by fundraising or volunteering for the first-time candidate and businessman in the last week of the race. Vice President Joseph R. Biden Jr. followed up with a radio ad for Murphy released Thursday.

Not to be outdone, Murphy’s Republican opponent, veteran New York Assemblyman Jim Tedisco rolled out his own big endorsement yesterday — from the Humane Society.