Biofuels in the US were mostly motivated by a desire to reduce oil imports ("energy security") and were a bipartisan misstep. The original mandate (7.5e9 gal/yr) was part of the Energy Policy Act of 2005, passed during a Republican trifecta, and was later expanded to 3.6e10 gal/yr by a Democratic congress in 2007 (still Bush - part of his "Twenty in Ten" energy security goal [0]). That said, reducing greenhouse gas emissions was definitely seen at the time as a benefit as well.

[0] https://georgewbush-whitehouse.archives.gov/stateoftheunion/...