不能说的秘密：米歇尔访华花费知多少？

You can see a video of First Lady Michelle Obama playing ping-pong in China, hear her talk about the importance of studying abroad and view a of picture of her huddling with her daughters with the Great Wall Of China snaking into the distance. What you won’t see, however, is a disclosure of how much her week-long trip in China cost.

The White House has a longstanding policy—that stretches back decades—of not commenting on the costs of trips taken by first ladies, vice presidents and presidents.

“We don’t discuss costs,” said Brian Leary, a spokesman for the U.S. Secret Service in a brief telephone interview. And in a pre-trip briefing for reporters, White House deputy national security adviser Ben Rhodes said “As a general matter, we don’t disclose the details associated with the security of either the President or the First Lady. This question comes up on many trips.”

Whenever the president and first lady travel, reporters generally ask about the cost and generally don’t get an answer. The reason given: security. If the White House or Secret Service tells the public how much a trip costs an enterprising person might be able to determine exactly what sort of security protections are used.

The last major report on the costs of presidential travel came in 1999, when the Government Accountability Office tallied up (or at least, tried to) the cost of President Bill Clinton‘s trips to Africa, Chile and China. To arrive at the numbers below, the GAO said it compiled information from the multiple agencies involved in the trip and did some calculations about hourly flight costs for the various military planes and helicopters involved in the trek, among other things.

Here are some interesting facts from that report:

-Mr. Clinton’s weeklong trek in China cost $18 million; his 12-day trip across Africa cost $43 million and his five-day sojourn in Chile cost $10.5 million.

-More than 500 personnel from the departments of Defense, State and Treasury helped support the trip to China.

-For each trip, officials from a variety of agencies travel to the country three times before the president arrives to deal with logistics and map out security plans.

-The bulk of the costs from the trips are for aircraft, such as Air Force One and other military support planes/helicopters.

-The total costs don’t include the expenses of the U.S. Secret Service. Their costs are classified, which means the actual cost of the trip is likely higher since they’re the main force protecting the president.

Steve Ellis, a spokesman for the government watchdog group Taxpayers for Common Sense, said after the Sept. 11, 2001 attacks it has been even harder to find out the costs of presidential travel.

That hasn’t stopped people from trying to estimate the expenses. In 2010, Mr. Obama went to India for several days and the White House had to bat away a report, first published in an Indian newspaper, that the trip was costing $200 million a day.

The White House said that number was wildly exaggerated, but still didn’t provide details about the actual expenses.

Mr. Ellis said it would make sense for the administration to release trip expenses after the president returns. “We’re not saying that the president or the first lady shouldn’t travel,” he said, but taxpayers deserve to know the cost.

In 2010, the public-interest group Judicial Watch caused a stir when it reported that Mrs. Obama’s vacation to Spain cost taxpayers about $450,000. Judicial Watch got the numbers after filing Freedom of Information Act requests with the Air Force and U.S. Secret Service.

About half the costs were related to travel expenses and the first lady (and president and vice president) don’t get to choose how they travel, the Secret Service does. That means if the first lady or president goes somewhere, even if on vacation, they take military aircraft instead of jumping on civilian aircraft. That helps explain why the costs are generally high.

Among the more trivial costs listed in the documents: $57.68 for four bottles of maple syrup and a package of pancake mix purchased by the flight crew.