Knowing that a president existed doesn't make one a good source. So, knowing that Jesus existed doesn't make one a good source about Jesus. Since the internet didn't exist in those days, and since there were not reporters (that we know of) snapping pictures of Jesus and recording his voice, it is difficult to have reliable info. Since the bible was written at least 100 years after the apostles had died, it is difficult to get accurate statements from them. It is possible that the info was transferred by word of mouth. But that is not very reliable. It is also possible that God told people what to write in the bible (by divine revelation). But, if so, the bible would be 100% correct, since God is presumed to be 100% correct. But then how did all of the errors in the bible get there?
Example of contradictions in the bible:
Gen 1:25: Man created before animals.
Gen 2:18: Man created after animals.
It could be that God wrote it 100% correctly, then some king or pope rewrote the bible wrong.
But that would mean that the bible is wrong.
If the bible is wrong, and the only reason for believing in God is what we read in the bible, then we don't have any basis for believing in God.
However, there is a way to be sure about God's divine revelation. That is to get the info right now directly from God, himself. Psychics claim to be able to do this.
On the other hand, Psychics in the bible (Revelation) said that the presidents who attacked Iraq are Satanic demons from the bottomless pit of hell. So, we are forced to conclude that if the bible is right, and if there is a God, current Christians who defy God (kill, while God commanded "thou shalt not kill" and don't turn the other cheek), must not be following God, but must be following Satan. Those who support the war in Iraq must be following Satan (because that is certainly not what God has ordered). You sort of know this is true because of the lies, cover-ups, and the torture camp at Guantanamo. All of this is not like God.