Personally I find it weird that they're trying to blame this on the Democrats in the article in. The dude served his sentence and was released for his previous offenses.
Now if Republicans allowed Democrats to have funding to treat his schizophrenia, then this event may not have happened. Even better if they would allow funding to actually house the homeless so they don't have to stay on trains all day.
Even if we listen to the Republican argument of being tough on crime, it doesn't make sense to give somebody a life sentence for a single assault. At some point this person will have to be released in society, and it Would be extremely beneficial to society to fund mental health treatment for such people.