The U.S. has sent tens of billions of dollars worth of military aid to help Ukraine fend off Russia's invasion, but the effort is coming at the expense of aid the U.S. initially intended to send to Taiwan.

The backlog of military aid to Taiwan has grown by more than $4 billion since the U.S. began its effort to support Ukraine's military in February, according to the Wall Street Journal. Russia's invasion of Ukraine already raised fears that China could use the opportunity to invade Taiwan, and the lessened support from the U.S. may only exacerbate the potential.

The U.S. has sent nearly $20 billion in military aid to Ukraine since February, so much that President Biden's administration is struggling to keep track of how the aid is being used. The volume of U.S. aid to the country has given rise to some skeptics within the Republican Party, who are calling for greater accountability.

Congress is reportedly making an effort to shore up its support for Taiwan with a fast-tracked funding package aimed at making the island more readily prepared for an invasion than Ukraine was.

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A dog and Ukrainian army soldiers in the street on the outskirts of Kyiv.

A dog is seen in the middle of a street as Ukrainian army soldiers take part of a military sweep to search for possible remnants of Russian troops after their withdrawal from villages in the outskirts of Kyiv, Ukraine, Friday, April 1, 2022.  (AP Photo/Rodrigo Abd)

China has grown increasingly aggressive toward the self-governed island in recent years, conducting weeks of military exercises in an apparent simulation of an invasion this fall. Chinese President Xi Jinping has warned that Taiwan's reunification with mainland China is a top priority and has not ruled out using force to do so.

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Taiwan first split from mainland China in 1949 after pro-democracy forces lost a civil war against the Chinese Communist Party. The democrats then fled to Taiwan and have governed themselves there for decades.

Taiwan military

Taiwan military forces conduct anti-landing drills during the annual Han Kuang military exercises near New Taipei City in Taiwan on Wednesday, July 27, 2022. A group of Japanese lawmakers including two former defense ministers met with Taiwan's president on Thursday in a rare high-level visit to discuss regional security. (Taiwan Ministry of National Defense)

Nevertheless, China refuses to accept the island's independence, and uses its economic weight to pressure the world to do the same. The U.S. has long abided by its One China policy, which states that the U.S. acknowledges the government in Beijing as the true government of China. It also states that the U.S. will not hold formal diplomatic relations with Taiwan.

President Joe Biden walks toward Xi Jinping

President Biden reacts as he walks to greet Chinese President Xi Jinping before a meeting on the sidelines of the G20 summit meeting, Monday, Nov. 14, 2022, in Bali, Indonesia. (AP Photo/Alex Brandon)

While the U.S. does not have a formal embassy in Taiwan, it has long had extensive trade ties with the island and delivered defense supplies.

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The U.S. has adopted a policy of "strategic ambiguity" regarding Taiwan and its relationship with China. Biden himself has vowed on four separate occasions that the U.S. would deploy its military to stop an invasion should one take place, but the White House has walked back his comments each time.