We only entered the War after Pearl Harbor.
Looking back some may say we should have focused on Japan first because nearly 70,000 Americans were being held as POWs at the time and being tortured.
In the mean time Hitler would have crushed the Russians and therefore elimnated an enemy for us. The problem was that we didnt know how long the UK would last and we could not afford to lose them as an ally. So we focused on Germany first. WW2 had nothing to do with saving the Jews if it did then we would have bombed the railways leading to the concentration camps, and even bombed some of the camps themselves. That would have deeply hampered the Nazi killing machine.
" In the mean time Hitler would have crushed the Russians and therefore elimnated an enemy for us."
There are some arguments that if Hitler had not personally overridden the wishes of his military command regarding strategy in the invasion of russia, targetting moscow vs. more emphasis on southern oil fields, not allowed any retreat for the russian winter, etc., he might have defeated russia anyway. In this matter he appears to have saved stalin from defeat as a consequence of his own massive purging of his officer corp in the years leading up to the war and the impact that had on the soviet military's ability to function during the german invasion.