The move comes after Republicans have fanned speculation that national Democrats are turning their attention away from Florida, where most polls show Murphy trailing Rubio.
The Democratic Senatorial Campaign Committee earlier confirmed it had reduced a week’s worth of TV spending in Florida at the end of September.
Instead, the new spot airing today in the state challenges Rubio’s support for Social Security and Medicare — one of the most popular whistles to sound in an attempt to drive older voters to the polls.
The Senate Majority PAC is putting the biggest share of money into the ad, the first wave of major advertising expected to carry into Election Day. Also financing the spot is AFSCME People, the American Federation of State, County and Municipal Employees’ political action fund.