The fight between GOP presidential candidates Ted Cruz and Marco Rubio continues to heat up. Cruz set things off last week with a direct hit against Rubio over the latter’s support for the Gang of 8 immigration plan, an attack that the Rubio camp seemed ready for. This week, their debate has moved on questions of surveillance and homeland security in the wake of the ISIS attacks on Paris, and it’s Rubio who’s the aggressor.

At a Monday forum hosted by the Wall Street Journal, Rubio criticized his fellow senator as he discussed the threats to Americans from both organized terrorist groups as well as “lone actors” working in the country.