Why is the U.S. buying helicopters from Russia?

Ten senators—eight Republicans and two Democrats—called on President Barack Obama last week to respond more forcefully to the incursion into the Crimean Peninsula by terminating the remainder of a $1 billion contract to buy helicopters from Russia.

In a letter to the president, the senators pointed to the Pentagon’s purchase of Russian-made Mi-17 transport helicopters for Afghanistan’s national security forces. About two dozen of 63 helicopters ordered have not yet been delivered, according to the letter. The Pentagon had already trimmed the original order for 78 helicopters last year in response to pressure from Congress.

Dozens of members of Congress have long pushed for an end to the Pentagon’s contract with Russia’s arms export agency, Rosoboronexport. Russia’s “illegal invasion of Ukraine and annexation of Crimea” provides an even broader reason to kill the deal, the senators wrote in the letter to Obama.

The senators also want Obama to impose sanctions banning any future U.S. business with Rosoboronexport. They describe the agency as “unsavory” because it has supplied Syrian President Bashar al-Assad’s military forces with arms and ammunition that have been used against Syrian civilians.

By obstructing Rosoboronexport’s business, “we would increase the costs of Putin’s aggression,” the letter said. The senators said ending the contract would limit the income corrupt Russian officials earn by skimming the profits of arms deals.

While acknowledging Rosoboronexport’s arms sales to Syria are deplorable, U.S. military officials have defended the Mi-17 contract. They’ve maintained the Russian helicopter is ideally suited for the Afghans, who are rebuilding their air force and need a reliable and easy-to-operate helicopter for transporting troops throughout the country. The fact that the Afghan forces had years of experience flying the Mi-17 figured prominently in the Pentagon’s decision to purchase the aircraft.

Neither the Pentagon nor the Army office in Huntsville, Ala., responded to questions about the contract’s terms and whether military officials have considered canceling it due to the crisis in Crimea.

Two Republican senators who signed the letter, John Cornyn of Texas and Dan Coats of Indiana, had wanted to use the Ukrainian aid bill as the vehicle for terminating the Mi-17 contract and sanctioning Rosoboronexport. But the amendment they drafted has yet to be considered.

The Associated Press contributed to this report.