Key issues at stake in potential US-Russia nuclear treaty renewal

Tactical nuclear weapons: these are usually short-range, designed for use on the battlefield, and generally left out of nuclear weapons treaties. Russia has about 1,477 non-strategic warheads, while the United States has about 200, according to the FAS. Putin has specifically mentioned tactical nuclear weapons as an issue.

Submarines: The United States has more strategic nuclear submarines than Russia.

China: Putin has said the US wants Moscow to get its ally China involved in arms control, though Moscow says it is up to Beijing and that, if China is involved, Britain and France should be too. The FAS estimates China has about 600 nuclear warheads and rising, but Beijing says it does not want to enter negotiations with countries that have much bigger arsenals.