Connor - the fights over the phrase "under God" have been around as long as I can remember - this is nothing new. The fact of the matter is that the phrase was added in 1954 during the Red Scare. Part of the reason was pressure from religious groups who, even then, wanted to redefine the US as an explicitly Christian nation, and part was to visibly differentiate the US from the officially-athiest Soviet Union.
As written by the Reverend Francis Bellamy (who was a Christian socialist and the brother of a socialist author) in 1892, the original wording of the Pledge was:
I pledge allegiance to my Flag and the Republic for which it stands, one nation, indivisible, with liberty and justice for all.
"...my flag..." was changed to "...the flag of the United States..." in 1922 and then to "...the flag of the United States of America" in 1923. This was explicitly to avoid confusing immigrants about which nation they were pledging to.
In a related topic, the official motto of the US was changed from "E Pluribus Unum" to "In God We Trust" in 1956 for much the same reason as the change to the pledge. (The new motto actually started appearing on currency in 1864.)
Interestingly, neither change has ever been heard by SCOTUS. A pledge case did get appealed to them once, but they dismissed it rather than ruling on it because they determined that the plaintiff had no legal standing to file the suit. There have been a couple attempts by the GOP in the last ten years to strip SCOTUS of the power to determine the constitutionality of things like this, but they all died in the Senate. Odds are, however, that that law itself would have been determined to be in direct violation of the constitution. Personally I don't see what they're so worried about - the current makeup of the court all but guarantees the pledge would pass inspection were it to be reviewed right now; Eight of the judges always vote down party lines, and the last one votes conservative about 3 times in 4. One of them - Scalia - has ALWAYS pressed for the implementation of Biblical law and Christianity as the official religion.