Why did lincoln decide to give the emancipation proclamation even though he knew that the republican party would suffer in the 1864 election due to anger from northern democrats and border state unionists?

Though it didn´t mean immediate freedom for slaves, the Emancipation Proclamation had an enourmous symbolic power. It shifted the main purpose of the war from keeping the integrity of the country to a fight for freedom of slaves as one of the Union´s goals. It also discouraged Britain and France to intervene in the conflict in favor of the South to advance their interests. The proclamation also helped mobilize black men to enlist and fight in Union Army; some 200,000 black soldiers belonged to Union ranks by the end of the Civil War. So, as we see, there were some strategic goals and short-term gains that made Lincoln issue the declaration, despite some ulterior political losses he and his party may have suffered in 1864.

Explanation:

to force terrorists groups to stop attacking western targets using massive military force.