Republicans in Congress have asked Pentagon officials tough questions about tens of billions of US dollars in defense and other aid to Ukraine, raising doubts about their continued support for Kyiv.

Testimony from Defense Department officials to two House committees and questions from lawmakers just days after the anniversary of the Russian invasion raised concerns about the high cost of shipping weapons to Ukraine. Those doubts now threaten the rare partisan consensus that has been reached on aid to Kiev, as the Biden administration may struggle to win congressional approval for new funds that could even be cut off next summer.

Testimony before committees also showed that members of both parties are concerned about the ability of a small but egregious minority of conservative Republicans and progressive Democrats to undermine Kyiv’s legislative support.

“We are all concerned about returns on capital. We must make all the evidence public so the American people can be convinced of its rational use,” said Rep. Joe Wilson, D-S.C., during a hearing of government officials in the House Armed Services Committee.

Tensions came to the fore Tuesday when Georgia Rep. Andrew Clyde, a longtime critic of Ukraine’s funding, raised questions about the loss of arms supplies and allegations of fraud in the bailout process for Kiev.

Responding to accusations by Republican members of the committee, Pentagon Comptroller General Robert Stork testified that there were no reports of sensitive weapon systems being sent to suspicious recipients.

The White House’s commitment to supply Ukraine with advanced tanks and other weapons systems threatens to collapse the Pentagon’s budget. Last December, Congress approved $45 billion in defense and other assistance to Ukraine, estimating that the funds would be sufficient through September.

The unexpectedly high cost of the war prompted Congress to make a series of requests to the executive branch to account for spending on the Ukrainian army. This information, although received by members of Congress, was not made public.

Rising costs and a lack of detailed information have sparked controversy among many critics of aid to Ukraine, who have described the program as a failure in recent days.

Democratic lawmakers also raised concerns Tuesday, asking Pentagon officials to be honest about how much money Congress will still ask for approval in aid to Ukraine. “How many times do you think Congress should bail out? What is the long term strategy? ” said Rep. Colin Cal, D-Cal.

Similar “difficult” questions were asked by members of the Democratic Congressional Appropriations Committee responsible for overseeing the defense budget. “How much more will the costs be in the new bill? We should at least be prepared for this turn of events,” said Hawaii Democratic Rep. Ed Case.

However, the Pentagon leadership refrained from such assessments, refusing to provide a schedule for future requests for new funding. “I can’t predict if new spending will be higher or lower. All I know is that we are planning the combat-ready deterrence force that Ukraine needs,” said Undersecretary of Defense for International Security Affairs Celeste Wallander.

Last week, bipartisan lawmakers called on President Biden to supply Ukraine with F-16 fighter jets. However, the Pentagon warned that sending such planes would not boost Ukraine’s capabilities, as pilot training takes 18 months. Even sending older F-16s would be prohibitively expensive, with the total cost of 36 aircraft being $2-3 billion, far less than the 50-80 requested by Kiev.