Republicans in Congress could break ranks with President Trump and support impeachment if evidence emerges that he directly linked Ukraine military aid to an agreement by Kyiv to investigate political rival Joe Biden.

Congressional Republicans are skeptical Trump told Ukraine President Volodymyr Zelensky that assistance from Washington was contingent upon his government launching a probe of Biden’s dealing with Ukraine while he was serving as vice president. But Republican sources told the Washington Examiner Tuesday, just before House Speaker Nancy Pelosi announced an impeachment inquiry, that enlisting a foreign capital to target a Democratic presidential contender would constitute an abuse of power.

A Republican insider who has been privy to conversations on Capitol Hill said, “If there is evidence of a quid pro quo, many think the dam will start to break on our side.”