Which major US TV networks are commonly perceived as left-leaning and what evidence supports that?

1. Major networks commonly seen as left-leaning

Cable news networks most frequently labeled left-leaning are MSNBC and, increasingly in academic measures, CNN; the Annenberg/UPenn and Stanford-based visibility studies found both CNN and MSNBC shifted left over the last decade in guest ideology scores, while Fox moved further right ^{[1] [7]}. In parallel, mainstream broadcast networks—NBC, ABC and CBS—are often judged by conservative respondents to have a liberal slant, with Pew Research showing high distrust of NBC and CNN among consistent conservatives ^[2].

2. What “evidence” researchers and watchdogs use

Evidence rests on three distinct strands: automated content analytics that measure who appears on screen (visibility bias), polling about which outlets audiences trust or perceive as partisan, and third‑party bias ratings that synthesize expert and crowd input; each approach yields overlapping but nonidentical pictures of lean ^{[5] [3] [4]}. The visibility approach assigns ideology scores to on‑air guests via donation and affiliation databases and uses face recognition to estimate how often liberal or conservative actors appear, generating a quantitative signal of slant ^{[5] [1]}.

3. Findings from academic studies and research centers

A decade‑long cable analysis published by Annenberg and colleagues concluded Fox shifted right while CNN and MSNBC moved left, using guest donation records to infer ideology and screen time to infer emphasis—evidence that cable polarization has grown and that these networks’ guest ecosystems differ systematically ^{[1] [7]}. The University of Utah team likewise showed that bias varies by hour and program, undercutting any simple label that applies uniformly across a whole channel ^[5].

4. Polling and public perception data

Surveys show partisan gaps in trust that map to perceived lean: YouGov and Pew found CNN and MSNBC are trusted far more by Democrats than Republicans, with CNN showing one of the largest partisan trust gaps, and consistent conservatives naming Fox News much more often as their primary political news source ^{[3] [2]}. Pew polling also documents that consistent conservatives distrust NBC, ABC and CBS at high rates, which contributes to perceptions of a liberal mainstream ^[2].

5. Variability, nuance, and methodological limits

All of these signals must be read cautiously: visibility bias captures guest ideology but not editorial framing or choice of stories; audience polls are influenced by the “hostile media effect” (partisans see neutral coverage as hostile); and ratings schemes like AllSides combine crowd and expert input with their own decisions about scale—so “left-leaning” can mean different things depending on the metric ^{[5] [6] [4]}.

6. Competing explanations, agendas, and critiques

Critics argue that labeling networks “left” can be driven by political actors or commercial incentives—Roger Ailes famously framed Fox’s creation as a response to perceived liberal media, and right‑wing outlets have institutionalized alternative ecosystems ^[8]. Conversely, some scholars and outlets argue mainstream newsrooms skew liberal in workforce composition and sourcing choices, a point made in surveys and historical analyses though contested in scope and effect ^{[9] [8]}.

7. Bottom line

The defensible summary: CNN and MSNBC are commonly perceived — and by some empirical measures shown — to lean left relative to the broader broadcast and cable field, while NBC/ABC/CBS are often judged center‑left by conservative respondents; the evidence combines guest‑based visibility studies, trust polls, and bias ratings, but each method has limitations and none yields an absolute or uniform verdict across programs, timeslots, or story types ^{[1] [5] [3] [4]}.