What are U.S. options as Russia tightens grip on Ukraine?

Ukraine showdown: Crisis leads to clash of Co... 02:21

Russian forces are tightening their grip on Crimea, a vital region of Ukraine, as the United States and Russia go nose-to-nose in their biggest confrontation since the days of the Soviet Union.

The Obama administration is threatening Russian President Vladimir Putin with economic sanctions and the U.S. president's credibility is at stake, according to CBS News senior security contributor Mike Morell, a former deputy director of the CIA.

"The only thing that Vladimir Putin understands is tough (action), and there has to be a tough response for Putin to pay attention," Morell said. "The things we've done already are pretty weak and Putin will see them as weak. Military action is not an option for obvious reasons. The only real option is economic sanctions. That could bite the Russians, but do we really want to get into an economic war with Russia, with a country that produces the second-most oil in the world and a country that produces the second-largest amount of natural gas in the world? He can cause real problems."

U.S. pushes Russia to remove military in Ukra... 01:33
Morell said that the risk now is that war could spread. "Eastern Ukraine is largely Russian-speaking, and that could give Putin a reason to move into eastern Ukraine and have a larger war between Ukraine and Russia."

Asked why Putin is doing this, Morell said, "I think there's two reasons. One is, it's been long-time Russian foreign policy in general and Putin's desire in particular to establish control -- complete control -- over all of those states that used to be part of the former Soviet Union and it is also his strong desire to undermine the United States at any chance he can. So moving into Crimea sends a very powerful message not only to Ukraine but to all of those countries of the former Soviet Union, 'Don't mess with me.' And to do it a day after the president tells him not to, gives the United States a black eye."

Ukraine's new prime minister said that his country will not give up Crimea to anyone. He's accusing Russia of declaring war, and Ukraine's military is getting ready to fight.

Ukraine mobilizes as Russian troops control C... 02:53
CBS News' Elizabeth Palmer, reporting from a Ukrainian air force base in Sevastopol, Crimea, said the Russian foreign minister Sergey Lavrov has spoken up in Geneva, Switzerland, and has made it clear that Russian troops are going to stay in southern Ukraine until "the situation normalizes."

The Russians are in control in Crimea after a bloodless takeover that has lasted less than a week, but there are still pockets of resistance: Ukrainian forces barricaded inside their own bases, but they're surrounded by Russian military and hopelessly outnumbered. Some have already changed sides, including the head of the Ukrainian navy.

CBS News ran into others at the Crimean border yesterday, Elizabeth Palmer reported. "(They are) Ukrainian troops who had hoisted the Russian flag at their barricade," Palmer said. "They were backed up by a local militia who stole our body armor and told us to turn back. So we headed for the nearest railway station, and took the train.

"We've just crossed the border into Crimea and the train didn't even slow down," she continued. "There were certainly no checkpoints or controls, which goes to show you that until a couple of days ago anyway, Crimea was a completely integral part of Ukraine. All that has now changed. This is occupied territory, and it's got the Western part of the country on the streets protesting.

"In Odessa, thousands marched against the Russian invasion, and in the capital, Prime Minister Arseniy Yatsenyuk, called the invasion a declaration of war," Palmer reported.

Yatsenuk said, "And Russia is to realize that they will pay the price. And not only Russia, but those who are to date in Crimea and they present an illegal...power in Crimea."

Ukraine crisis: What role should the United S... 13:16
Palmer is currently reporting in an area where the resistance still stands -- on a Ukrainian air base where Ukrainian soldiers are standing their ground. However, Russian soldiers have been at the base's gate and have demanded that the soldiers leave the base on Monday. "Nobody knows exactly what the implied 'or else' is, nobody knows what's going to happen next, but it's very tense indeed," Palmer reported.

Secretary of State John Kerry is going to Ukraine Monday night. On Sunday, Kerry told Bob Schieffer on "Face the Nation" that Russia has committed an "incredible act of aggression." He said, "You just don't, in the 21st century, behave in 19th century fashion by invading another country on completely trumped-up pretext. I think Russia needs to think very carefully about the choice that it's making. And there are visa bans. There are asset freezes. There is isolation with respect to trade and investment. American businesses may well want to start thinking twice about whether they want to do business with a country that behaves like this. These are serious implications."

President Obama spoke with other world leaders on Sunday. White House officials say they're prepared to shut out Russia.

White House considers sanctions against Russi... 02:36
CBS News chief White House correspondent Major Garrett reports that the economic moves that Kerry outlined are very real and the White House is hoping that Russian President Vladimir Putin will back down, at least slightly, and take the offer now on the table of international observers and international monitors in Crimea, instead of risking long-term economic isolation.

Everything the U.S. has done so far to punish Russia -- canceling high-level talks on trade and energy expansion, canceling preparations for a G8 Summit in Sochi, Russia -- are temporary and can be easily reversed, but if the U.S. and its allies hits Russia with economic sanctions or deny Moscow's access to global financial networks and key international banking accounts, the damage to the Russian economy could be long-lasting and it could put U.S.-Russian relations in the deepest, most confrontational stance that they've been in during the entire Obama presidency.

The administration believes Putin has overplayed his hand and will not fire shots in Crimea and not move his Russian forces into less friendly parts of Ukraine. With Canada, Great Britain, France, and Germany all against Russia's, Moscow's own status in the G8 is also in jeopardy. These nations are also preparing, along with the United States, for an economic package to rescue the transitional and fragile government in Ukraine.

The U.S. doesn't need or want to punish Russia, necessarily, for this violation of international law. The U.S. just wants Moscow to back off and ease the tensions, but right now, Russian forces are there in Crimea, and until they move out, this is going to be a confrontation between those Russian forces on the ground and the implied threat of economic sanctions in the West.