I've seen this repeated a few times, but it needs to be pointed out: it wasn't Trump who "repealed the regulation to update train brakes".

To make a long story short, there was a Regulatory Impact Analysis that found the cost of ECP brakes would outweigh the expected benefits. So, according to the FAST (Fixing America's Surface Transportation) Act that was passed under Obama, the DOT were required by the bill itself to repeal the requirement.

Something else to note is that ECP brakes were designed entirely around preventing collisions and would have done nothing to prevent an on-rail derailment of the train. Likewise, the fact that every single train car would have to be fitted with ECP brakes (as having a mixture would heavily impact network fluidity) is likely what heavily influenced the cost portion of any cost/benefit analysis. Combine that with the need for operators to spend more time between cars, and any benefit starts to shrink.

Never mind that Biden and Pete Bootychug had two fucking years to do something about if they really thought it was an issue.