I know I made the original "dwindling funding" claim, but it's actually a red herring. I should have said something like "increasingly competitive nature of grants". The argument relevant to this article is NOT about whether there's enough funding for science. Rather, the argument is about how difficult it is to get funding. I think it's fairly uncontroversial (and correct) to say that getting good science funded has become considerably harder over the years. I'm not sure anyone has done the work of trying to quantify that; maybe someone else can help find data for that.

But to address your question anyways:

1. USFG scientific funding instutitions are only one source of science funding. There are many others. If you look across the federal government, there's a downward trend: http://www.aaas.org/sites/default/files/DefNon%3B.jpg

One must also take into account non-federal-governemnt sources, which in many cases have substantially decreased their investments in R&D since 2008.

2. As pcnt of GDP there's been a steady decline: http://www.aaas.org/sites/default/files/RDGDP%3B.jpg

3. From an impact-on-culture perspective -- which is the relevant one in my comment -- I think (2) is more intresting than your data and also more interesting than (1). The question should be "how difficult is it to fund good science", not "how much are spending in absolute or relative terms". This is, of course, very difficult to quantify. But looking at percentage of GDP is at least better than looking at absolute dollars.