The late-night TV audience appears to be splitting into two distinct groups, ratings data out Tuesday reveals.

While “The Late Show with Stephen Colbert” attracted more total viewers for the 12th straight week — widening its lead last week over its NBC rival — NBC’s “The Tonight Show Starring Jimmy Fallon,” for the week ended April 21, widened its lead in the demographic favored by advertisers.

So the younger 18-to-49 demo appears to be turning away from Colbert’s anti-Trump-centric show while older viewers are still tuning in the CBS show.

Fallon’s 0.64 rating in the demo beat Colbert’s 0.45 rating by 42 percent. This gave “Tonight” its biggest demo win since the week ended Jan. 13.

As for total viewers, Colbert’s average of 2.83 million exceeded Fallon’s average of 2.59 million by 9 percent.

The demo victory by “Tonight” — the largest margin since the inauguration — indicated to some TV experts that politics, as satirized by Colbert, was losing its appeal for the under-50 set.

Yet Colbert’s political barbs continue to attract older viewers to a degree that suggests late-night viewing may be bifurcating by age group.

Last week’s victory also secured CBS’ longest late-night winning streak since another 12-week stretch that began on Oct. 26, 2009, and ended on Jan. 15, 2010.