[snewman]

A common scenario in many locations in the US:

A district tilts heavily toward one of the two main parties -- it is a "safe" district for that party. The candidate nominated by that party in the primary election is nearly certain to win the general election. If the candidate is highly extremist / flawed, they might lose, but party affiliation is sufficiently strong nowadays (aka the electorate is sufficiently polarized) that a candidate can be pretty far to one extreme -- farther out than the bulk of the electorate -- and still win.

Meanwhile, there is a tendency for the more centrist voters in both parties to skip the primary. Thus, the candidate who survives the primary is often relatively extreme.

The result is that the victor of the general election is often to the extreme side of not only the electorate as a whole, but the membership of their party.

To oversimplify, imagine that political views fall on a one-dimensional spectrum ranging from 0 to 1, and the electorate consists of:

  - 40% at 0.4 (center-left)
  - 30% at 0.6 (center-right)
  - 30% at 0.8 (heavy right)

In the primary, center-right voters are under-represented, and a candidate at or beyond 0.8 has an excellent chance of being nominated. Then in the general election, at least 2/3 of the center-right voters are likely to swing toward that candidate (because of polarization / strong party affiliation).

[nickff]

Looking at your spectrum, I'd see the same distribution as:

- 40% left

- 30% center

- 30% right

Any rating of 'how far' someone is along the spectrum is arbitrary, as the spectrum itself is arbitrary. I wouldn't see any extremism either.

[snewman]

Agreed, the spectrum ultimately is arbitrary. I was thinking in terms of a spectrum normalized to the country as a whole. In a particular district, you often have a breakdown that is off-center relative to the overall nation (of course that can be in either direction).

And in any case, the key point is that the primary process can lead to a candidate taking office who is well off-center even within their district.