In 1907, during the administration of Theodore Roosevelt, gold coins were coined without the "In God We Trust" motto, which leaded to numerous protests, and the President answered in a letter, stating that he opposes the usage of the motto in the coin, and explaining why:
"To put such a motto on coins (...) is in effect irreverence, which comes dangerously close to sacrilege. A beautiful and solemn sentence such as the one in question should be treated and uttered only with that fine reverence which necessarily implies a certain exaltation of spirit"
However, he was not opposed to use the motto in national monuments or certain other important governmental buildings, since in these places "it will tend to arouse and inspire a lofty emotion in those who look thereon."
He also states that removing the symbol was not unconstitutional, since there was no legal warrant mandating it at the time, according to him.
So, Theodore Roosevelt was for removing this motto for the coins (but not governmental buildings) not because he somewhat opposite the motto or religious symbols, but because he felt they were too solemn for mundane usage on coins - not the reason a modern secular activist would like...
About modern politicians, I found this guy, Sean Faircloth, a Democrat from Maine, who was a State Senator and a member of the Maine House of Representatives. He opposed a resolution that would "reaffirm" the phrase as the official motto of USA, calling to display it publicly in all governmental buildings. Not exactly about removing the existing usages of motto, but is a public opposition by an American politician:
“To me, as a former legislator myself, I was always skeptical of this kind of symbolic resolution,” said SCA Executive Director Sean Faircloth, who served for a decade in the Maine State Legislature, his last term as the Democratic majority whip.
While it may score political points for its sponsors, Faircloth contends, it also sends an inappropriate message that the religious views of certain Americans stand superior to others. He argues it is a message that some Founding Fathers such as James Madison also would have objected to.