(transitive) To cause to become obscure or muddled.
(transitive, usually passive) To cover or surround with clouds.
(transitive, figurative) To cast in a negative light, cast a pall over, darken.
1856, Abraham Lincoln, speech given on 19 May, 1856 in Speeches and Letters of Abraham Lincoln, London: J.M. Dent, 1907, p. 46,
We live in the midst of alarms; anxiety beclouds the future; we expect some new disaster with each newspaper we read.