Either is fine, and it depends if you're talking about one spineless person or lots of spineless people.
The Democrats are like the spineless [people that infest this world] who won't stand up for themselves.
The Democrats are like the [generic] spineless [person] who won't stand up for himself.
These are subtly different in their implications, but they basically mean the same thing and they both work.
On the other hand, I would personally always go for "themself" in the latter case rather than "himself" because women can be spineless too.
The Democrats are like the spineless [people that infest this world] who won't stand up for themselves.
The Democrats are like the [generic] spineless [person] who won't stand up for himself.
These are subtly different in their implications, but they basically mean the same thing and they both work.
On the other hand, I would personally always go for "themself" in the latter case rather than "himself" because women can be spineless too.
