The phrase "simmering debate" refers to an ongoing and unresolved argument or discussion that is intense, but has not yet reached a boiling point or final resolution. Full definition
A long - simmering debate over how rigorously to protect other planets from Earth life, and how best to protect life on Earth from other planets, is coming to a boil. (sciencenews.org)
Brown, who issued his unity call a day before the party's committee members were set to gather for their annual meeting, explained why he decided to entered this long - simmering debate now — even though the 2018 elections that will officially determine the make - up of the Senate are over a year away. (nystateofpolitics.com)
In 2016, a long - simmering debate erupted into a roiling boil. (discovermagazine.com)