The Biddeford, Maine, office of Sen. Susan Collins, R-Maine, was vandalized Monday night for the second time in a month, Collins' chief of staff told Fox News.

After vandals previously spray-painted the building's door in September, saboteurs on Monday dumped a bucket of red paint in front of the location while writing in crimson — "BLOOD on her HANDS" — on the sidewalk in front of the building.

"This is another incident in a series and the second attempt at our Biddeford office to intimidate the Senator and her staff. These tactics are disturbing, but not effective. Our staff is undeterred and on the job," Collins' chief of staff Katie Brown told Fox News' Alexis McAdams.

The Biddeford office is near the scene of an Immigration and Customs Enforcement (ICE) officer-involved shooting in which a law enforcement officer shot and killed 26-year-old Colombian national Johan Sebastián Guerrero in July.

Days after the shooting, protesters barged into the Biddeford office's front door, chanting "vote her out." In September, the "Trump whore" epithet was spray-painted in red on her office door.

Collins' challenger for her U.S. Senate seat, former Democratic state Senator Troy Jackson, condemned the September vandalism in a statement to Fox News Digital.

"Senator Collins and her staff should be able to do their jobs without anyone defacing their office, and I condemn whoever did this," Jackson said. Biddeford police are investigating the incident, according to Collins' campaign.

Sen. Collins' and Troy Jackson's campaigns did not immediately respond to Fox News Digital's request for further comment.