The ongoing controversy surrounding Taiwan’s request to purchase sophisticated weapons systems from the United States, including 66 advanced F-16 jet fighters, continues to roil. In late July, President Obama capitulated to the demand of Senator John Cornyn (R-TX) and other pro-Taiwan members of Congress to have the Pentagon complete its report on the issue by October first and make a prompt decision thereafter. For weeks, Cornyn had held up the appointment of William Burns as deputy secretary of state until the administration agreed to his terms.

Even though a favorable decision on the arms purchase request would undoubtedly anger China, it is probable that the White House will approve the sale. Domestic economics and politics will play at least as much a role as sober foreign-policy considerations. Portions of the F-16 are manufactured in some 44 states, and the plane is assembled in Texas (which may explain Cornyn’s especially intense interest). That is not a minor consideration for an administration plagued by a persistent economic recession and facing a tough election year in 2012.

A decent case can be made on foreign-policy grounds for approving the sale of advanced weapons to Taiwan, and I have made that case in previous writings. But such a decision should always be based on a careful cost-benefit calculation. As China has grown stronger and become more important economically and diplomatically to the United States, the potential cost to Washington of angering Beijing has risen.

An especially troubling aspect of Senator Cornyn’s pleasure at the administration’s capitulation was his statement that the United States had an obligation to stand by “one of our good allies, a democracy.” That attitude is perilously close to viewing foreign policy as a risk-free expression of ideological solidarity.

Cornyn’s view is wrong on two counts. First, the security commitment to Taiwan, symbolized by continuing arms sales, is anything but risk free. China is committed to Taiwan’s eventual political reunification with the mainland. Washington’s insistence on thwarting that objective and perpetuating Taiwan’s de facto independence risks, at a minimum, severe diplomatic strains and could at some point risk a disastrous military clash.

Second, Taiwan is not an “ally,” good or otherwise. It is a security dependent—a client state. The island is simply not powerful enough to make a significant contribution to America’s security. The informal defense relationship all flows one way. Like it or not, Taiwan is a protectorate, not an ally, of the United States.

Unfortunately, Senator Cornyn’s sloppy equation of a weak security dependent with a valuable ally is all too typical of foreign-policy thinking in Washington. During the Cold War—and even more so since the end of that struggle—the United States has added an assortment of weak (and often vulnerable) security clients. One need only look at the list of America’s NATO “allies”—especially the various mini-states in the Baltics and the Balkans—to confirm just how useless most of them would be to the United States in a serious conflict.

Such so-called allies are security liabilities, not assets. Commitments to defend them expose the United States to various headaches and dangers while providing, at best, modest potential rewards. Taiwan is already in that category, and as China’s economic and military power grows, America’s military relationship with the island state will become more and more perilous. Whatever President Obama’s ultimate decision on the current arms purchase request, this unpleasant reality will not go away.