Governments will try to get away with almost anything during wartime. In the Civil War, President Abraham Lincoln suspended the writ of habeas corpus so federal authorities could lock up suspected Confederate sympathizers and throw away the keys. This action was more than mere ink on paper; it was very vigorously enforced, especially in Maryland and other Border States. He also signed the Revenue Act of 1861, which put an income tax into effect. The government gave up in 1862, partially due to Constitutional concerns regarding the Apportionment Clause (all taxes must be apportioned between the states), but mostly because the Revenue Act simply didn’t raise much money.
Congress took care of that Constitutional technicality with the 16th Amendment in 1913. But it wasn’t until 1943 (yet another war) that the money started rolling in. (See Video Read more