Russia and Ukraine have been fighting since 2014, mainly in the Crimean peninsula and the Donbas region of eastern Ukraine. The U.S. government has been providing military aid to Ukraine since that time. Although $391 million in aid had already been approved in the fiscal year 2019 federal budget, and the Trump administration told Congress in February and again in May that it was releasing the aid, the aid was not released until September 11—almost at the end of the 2019 fiscal year.
Democrats maintain that Trump withheld the military aid to Ukraine so as to pressure Ukrainian President Volodymyr Zelenskyy to investigate former Vice President Joe Biden's son.
According to an article published by the Heritage Foundation—a conservative think tank that supports U.S. military aid to Ukraine:
Ukraine has rebuilt its once dilapidated military into the second-largest standing land army in Europe in terms of manpower. Today, after more than five years of war, Ukraine remains one of the world's top weapons-exporting nations and is able to meet many of its own defense supply needs.