Fall 1856
Caswell ran for the legislature as an independent Democrat and fell about a dozen votes short of election.
Nation and worldGrade A · 1 independent source
The evidence
“I was reared a Democrat and somewhat disposed to take a hand in politics. I ran for the legislature in the fall of 1856, not as a democrat but as an independent democrat, but I lacked a dozen votes or so of an election. A democrat at that time was so under suspicion of being in sympathy with slavery that his prospect of being elected to a political office was not over bright.”
1900-caswell-reminiscences/10-politics-and-congress.md, PDF pp. 3–27
Caswell, Lucien Bonaparte. The Reminiscences of the Hon. L. B. Caswell. Written at Fort Atkinson, Wis., 1914–1916; four-column newspaper reprint, newspaper and date unidentified. University of Wisconsin-Madison Libraries.
Grade A: Found on a page of one of our sources