In the debates, both were quite disappointing. Both candidates showed a remarkable ignorance towards the first amendment. Ms. O'Donnell asserted, as many fundamentalists believe, that the separation of church and state was externally imposed by court decision, and challenged anyone to show her that this principle is in fact in the constitution. Mr. Coons challenged her on this, but was then unable to mention any of the other protections of the first amendment. (Right to free speech, right to free press, right to redress the government, right to peaceable assembly.) Both have shown a shocking ignorance of the nation that they hope to regulate.
As for Ms. O'Donnell's assertion, she will be quite pleased to hear that the phrase "separation of church and state" does not appear literally in the constitution as such. However, the concept exists from the first amendment's statement that "Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof." Thomas Jefferson, who wrote that amendment, later wrote a letter describing his intention to have a "wall of separation between church and state," using those exact words.
Further connecting this, after the Barbary Wars, fought by the generation of Americans who founded the country, we signed the Treaty of Tripoli with the Barbary States. The treaty had 12 components, and in number 11, we assured them that we would not attack them for being Muslims:
As the Government of the United States of America is not, in any sense, founded on the Christian religion; as it has in itself no character of enmity against the laws, religion, or tranquility, of Mussulmen; and, as the said States never entered into any war, or act of hostility against any Mahometan nation, it is declared by the parties, that no pretext arising from religious opinions, shall ever produce an interruption of the harmony existing between the two countries."Mussulmen" and "Mahometan" being the 18th century way of describing Muslims. Essentially, we assert to being a secular nation that has no beef with Islam. I would further remind Ms. O'Donnell that treaties bear the same weight legally as the constitution itself.
The founders did seek to prevent what they saw as the abuse of religion at the time, in which the Church of England was quite embedded in the English government, and enforced its decrees with the force of the nation. They also felt that this diminished the honor of religion, especially when it became involved with the usual petty disputes that nations have to deal with. (Who owns the house on 1329 Main Street?) Someone always went away mad. To give the church government powers, in their minds, suggested that it was so weak that it would not survive on its own merits.
Since I wrote this, Delaware elected Coons instead of O'Donnell, by about a 16% margin.