article: with a history

[redgiant]

In all of those cases, we saw two senators with a history of supporting scientific research at every opportunity. And for those worrying whether Obama or McCain could afford to fund research in the current economic climate, they can take heart that the government spends so little on scientific research that cutting it wouldn’t really make that much of a difference anyway.

I don't understand why singular is used here.It says that Obama and McCain both have their history of supporting research, so it should be two histories from two persons, why "with a history" is used here? Or it is just a common usage or term?

[2006]

Originally Posted by redgiant

In all of those cases, we saw two senators with a history of supporting scientific research at every opportunity.

I don't understand why singular is used here. It says that Obama and McCain both have their history of supporting research, so it should be two histories from two persons, why "with a history" is used here? Or it is just a common usage or term?

If you say 'two senators with histories', it suggests that each senator has more than one history. Also consider the example below.

They both have a bad knee. (= Each one has one bad knee.)
They both have bad knees. ( Maybe each one has two bad knees.)