Ukrainains are putting up a fight against Russian invaders, but they still need more help, and are asking for foreign aid, including requesting membership to join the European Union.

Serhii Plokhii, director of Harvard's Ukrainian Research Institute told Jim Braude on Greater Boston that Ukraine is appreciative for the support they have received, but more assistance is needed. "The one specific issue that they want is to 'close skies' over Ukraine... that is the most immediate request," he said.

Plokhii has family and friends back in Ukraine, including his sister. "It's very tense. There is shelling in the city where she lives," he said.

In the fight against Russia, Ukrainians have overcome political differences that previously divided the country, according to Plokhii. "Now, all political parties, all major leaders, military and civilians are behind President Zelenskyy."

If the worst happens and Zelenskyy is replaced by Russian leadership, Plokhii said, "no government, president, parliament, any kind of government, would be considered legitimate by Ukrainians."

Watch: Ukraine asks for foreign aid in fight against Russia