During the War between the States Lincoln was known to instruct his military commanders to furlough registered Republicans while keeping Democrats (and any others) in the field, where they could not vote. In border states like Maryland, where there was powerful opposition to the war, federal soldiers flooded the cities on election days and were instructed to vote, even though they were not residents of those states. In the 1862 election, the Republicans lost seats in Congress and barely retained their majority because of the opposite of what you say -- so many Republicans were in the army and not at home to vote.
In the 1864 election the Republican National Committee was so certain that Lincoln would lose, they actually asked him to step down so a new nominee could be selected.
You've been duped.
Walt