The Lesser of Two Evils

Why do Christians justify "their" unrighteous politicians as preferable to the unrighteous politicians of "the other side" ?  Is it God's moral command to choose "the lesser of two evils" ?

"...why not say...as some claim that we say, 'Let us do evil that good may come' ?"  (Romans 3:8)

Why do Christians excuse their favorite politicians' doing evil on politicians promise that good ("pro-life" courts, for example) will come of it ?

God's promise to evil-doers, and those who justify them in evil, is infinitely more certain than that of the politicians: "Their condemnation is just" (ibid).