With the migration crisis, spot checks have been introduced at a few select crossings, but that still leaves plenty of possible train routes within Schengen where the authorities are not concerned about checking for migrants.

Or any excuse a Member State wants to justify their “temporary” checkpoint.

Don’t worry, MEPs won’t do anything more than talk about it.

https://ec.europa.eu/home-affairs/what-we-do/policies/border...

I've also seen it done for drugs on the Swiss border (this was on a night train actually) and twice at Berlin airports. They're rare but still happen.

Also unfortunately in between Copenhagen and Malmö, although a European ID card is fine as well.