Do Mainstream Party Positions Cause Far-Right Support?

Far-right parties have surged across Western democracies, and one explanation is that mainstream parties leave voters unrepresented by adopting positions more liberal than their electorates. We isolate this positional channel in an information-provision experiment with 5,040 Germans during the campaign preceding the 2025 federal election. Truthful, randomized signals shift beliefs about the center-right CDU's immigration position equally strongly across the electorate, leaving respondents' own attitudes and beliefs about other parties essentially unchanged. Political responses are concentrated among voters with restrictive immigration preferences. For these voters, a signal portraying the CDU as one unit more liberal raises AfD vote intention by 1.7 percentage points. Instrumental-variable estimates imply an increase of 3.5 percentage points per unit of perceived CDU position; an estimator that gives equal weight to voters who update toward the information yields 4.7 percentage points. Liberal and moderate voters show no comparable response. Felt representation changes in the two directions predicted by spatial voting: a more liberal perceived CDU position reduces representation among restrictive voters and increases it among liberal voters. The substitution extends beyond stated intentions: voters with restrictive preferences reduce consequential campaign support for the CDU and become more likely to seek information from the AfD. Mainstream-party positioning shapes far-right support by determining which voters the mainstream leaves politically unrepresented.