A Democratic super PAC is making in a second six-figure investment on a television advertising buy in the Massachusetts Senate race, a person familiar with the buy confirms, a move that comes with Election Day fast approaching and polls showing Democratic Rep. Ed Markey's GOP opponent within striking distance.

Senate Majority PAC is adding $500,000 to its existing television ad buy. The group hit the airwaves last week with a spot that hits Republican nominee Gabriel Gomez over his position on Social Security. The super PAC initially put about $500,000 behind the negative ad.