Billions of dollars in emergency foreign aid to Ukraine, Israel and Taiwan is on hold, caught up in a clash between U.S. Senate Democrats and Republicans, as GOP negotiators demand border and immigration changes in the package.

The White House will step up its engagement with U.S. lawmakers trying to strike a bipartisan deal that would provide military aid for Ukraine and Israel while tightening U.S. border security, a Democratic senator said on Sunday.

Joe Biden has said he is willing to make “significant” concessions on border security to help push Ukraine funding through Congress.

The White House portrayed it as a step toward compromise. When President Joe Biden sent his request to Congress last month for aid to Ukraine and Israel, he included a request for more money to help with security at the border with Mexico,

The White House says a failure to approve more aid by year's end could have catastrophic consequences for Ukraine and its ability to fight.