PARMA, Ohio — As a proud Ukrainian-American, Taras Szmagala has worked for decades to elect Republicans, the party he associates with freedom. He ran an ethnic outreach program for Richard M. Nixon’s 1972 campaign and advised President George Bush as the Soviet Union crumbled, when Ukraine became an independent nation.

Mr. Szmagala, 83, will mark Wednesday’s 25th anniversary of statehood at a parade and festival on Saturday in this Cleveland suburb, where the blue and yellow flag of Ukraine flies along the main thoroughfare in “Ukrainian Village.”

But there is a pall over the festivities. His name is Donald J. Trump.

Ukrainian-Americans have felt at home in the Republican Party since Franklin D. Roosevelt and Stalin divided control of Europe at Yalta. But across the United States — and especially in swing state Ohio, where Mr. Trump became the party’s nominee — they are watching the 2016 presidential race with a mix of confusion and fear.

“The party’s dead as far as I’m concerned,” Mr. Szmagala declared.

As if Mr. Trump’s admiring statements about President Vladimir V. Putin of Russia and his questionable explanation of events in Ukraine were not tough enough to stomach, then came news that Paul Manafort, until last week Mr. Trump’s campaign manager, was tangled up in a corruption inquiry and designated to receive millions in secret cash payments from the party of a pro-Russian leader he had helped to elect.