Behind Trump’s Tough Talk on Russia and Putin, Doubts and Missing Details

President Trump’s new plan to send weapons to Ukraine and his simultaneous threat of harsh penalties on Russia’s trading partners reflect a dramatic shift in his position on the war, but his proposals leave key details unclear.

Speaking alongside NATO’s secretary general, Mark Rutte, at the White House on Monday, Mr. Trump said that Patriot air defense systems and other arms would “quickly” be transferred to Ukraine, which is in desperate need of more weapons to fend off Russia’s invasion.

Mr. Trump said the United States would sell those arms to European nations, which would ship them to Ukraine or use them to replace weapons they send to the country from their existing stocks.

But Pentagon officials said later that many details were still being worked out.

And experts doubted the credibility of Mr. Trump’s threat to impose 100 percent tariffs on Russia’s trading partners if President Vladimir V. Putin of Russia did not agree to a cease-fire within 50 days.

The scale of China’s mutual trade with Russia — nearly $250 billion per year, including huge oil imports — means that delivering on the threat would throw Mr. Trump into a showdown with Beijing. Analysts said it was unlikely that Mr. Trump would risk a renewed confrontation with the world’s second-largest economy over Ukraine, a country whose fate he has long said is not vital to the United States.

Mr. Trump is also notorious for setting deadlines that he does not enforce, raising questions about whether he will act if the 50-day timer he has set for Mr. Putin expires.