Congress undoubtedly did not want war, and would have spurned a request by TR for a declaration of war. However, I don't think that is the question. The question is whether TR could have unilaterally accomplished a *fait accompli* making war inevitable, whether Congress liked it or not. For example, in OTL TR said during the 1916 campaign that after the sinking of the Lusitania, had he been president he "would have seized every German ship docked in the United States, telling Berlin: 'Now we will discuss not what you will give but what we will give back."
https://books.google.com/books?id=iyfEIkl3hXcC&pg=PA212 (Would TR in fact have legal authority to do that as president? I don't know, but even if he doesn't, who is going to stop him?...)