Sen. Joe Donnelly, D-Ind., appears confident that Ukraine – with backing from the United States – will stand up to further incursions by Russia.
Russian President Vladimir Putin "understands one thing. He understands strength. And we have to show strength in return," Donnelly said Tuesday in a conference call with reporters.
Donnelly was part of a bipartisan congressional delegation that visited Ukraine on Sunday in the wake of Russia's takeover of the nation's Crimea region.
Describing Putin's government as a "thug-ocracy," Donnelly warned that any attempt by Russia to grab more of Ukraine "risks setting off catastrophic events. We stand with our allies in Ukraine that if Russia crosses that line, they'll be getting into a swamp that will be very, very difficult to get out of."
In the meantime, he said, the U.S. and its allies can cause "extraordinary financial damage" to Russia if they impose economic sanctions against its energy and finance sectors in response to the annexation of Crimea.
Donnelly, a member of the Senate Armed Services Committee, said the U.S. and NATO are talking about reviving plans to place a missile base in Poland.
And although Ukraine officials have not sought U.S. weapons, they have inquired about obtaining military communications gear, he said.
ITT Exelis and Raytheon produce military communications systems at their Fort Wayne plants.
The Obama administration has frozen U.S. assets of key Russians and banned them from entering the U.S.
The Senate is considering legislation this week to send financial aid to Ukraine and authorize more sanctions against Russia.
Residents of the Ukraine capital, Kiev, told Donnelly during his visit that they "will fight for every square inch of the country," he said.
"Every single person who came up … and they would ask, 'Are you U.S.?' I said, 'Yes, I am,' and they said, 'We will fight,' " Donnelly said Tuesday. "It was not just one person or another person, it was waves of people coming up and saying that."
Even if Russia's military is far superior to Ukraine's, "there'd be very, very significant pain inflicted on Russia as well" in the event of fighting, Donnelly said. "And Mr. Putin would have to explain to Russian moms and dads why their sons and daughters never came home from Ukraine."
The congressional delegation that visited Ukraine included Sen. Kelly Ayotte, R-N.H., and Rep. Stephen Lynch, D-Mass.
The group also made stops in Israel and Afghanistan last week.
The lawmakers met with Afghan President Hamid Karzai and U.S. Marine Gen. Joseph Dunford, among others.
" … It is clear that we are on schedule to come home," Donnelly said about plans to remove all U.S. combat forces from Afghanistan by the end of 2014.