Not in a First-Past-The-Post voting system, which is used in most of the US (&afaik, in all presidential elections).

The 1PPP systems systemically trend to metastable 2-party states. Of course 3rd parties will have distinctions from their closer main parties, but it is almost impossible that a 3rd party will triangulate exactly between the two major parties.

This means that in practice, a vote for a 3rd party is effectively a vote for your worst major party option. The 3rd party acts as a spoiler - always.

This is NOT true in Ranked Choice Voting systems. There, the 3rd party spoiler issue goes away, and the 3rd parties have a real chance of being able to get elected & have a real influence.

To have the effect you want (vs some perverse effect), you must vote strategically in the system you have.

That said, it is long past the time that we implemented a few upgrades from the systems of 200 years ago, such as upgrading to Ranked Choice.

I'm not talking strictly about election results. I'm talking about ideologically. I do agree with you if your only concern is election results.

Yes, from the ideological push perspective, losing a crowd to a 3rd party might cause a major party to move in that direction.

I certainly prefer a number of 3rd parties for a number of reasons, but not until we get off the 1PPP voting system. Ranked Choice, or any of a number of other options, but the role of 3rd parties as spoilers is just too great.

The problem is that doesn't appear to happen in practice.

For example, how did Trump winning in 2016 help your average Green Party supporter achieve more of the change they wanted in the aligned Democratic Party?

Perhaps a better example is the UKIP party swaying the Tories to become more isolationist, and eventually triggering the Brexit referendum? A little bit different, knowing the political system of the UK enables smaller parties to be successful in a way the American system doesn't. But the principle is still the same. UKIP acting as a spoiler is factored into the strategy of the Tories policy makers, and thus they pivot their policies more in line with UKIP ideals to prevent bleeding voters to UKIP. A similar dynamic is at play on Canada's left-wing between the Liberals and the NDP

Brexit was about Tory backbenchers, not UKIP.

I'm not saying it happens in practice, I'm saying that's often the goal.

So you agree that it's a silly idea that doesn't actually work?

Doesn't work for what?