Although Trump has publicly endorsed the bipartisan prison and sentencing reform bill, he hasn’t publicly called out McConnell for bottling it up and seems reluctant to spend political capital on the legislation — raising doubts among bill supporters and opponents about how invested Trump really is. Indeed, the president is far more interested in securing money for his border wall in the lame duck, according to senators in both parties.

“We can certainly use his help in the Republican Senate caucus,” said Minority Whip Dick Durbin (D-Ill.), who conceded that Trump’s priority is the wall.

“I keep hearing that’s he’s all for it. I haven’t seen any evidence of that,” said one GOP senator who supports the measure to reform federal prisons and sentencing guidelines.

For lawmakers, the issue has highlighted the difficulty of working with the president on legislation. Aside from immigration and trade, the president holds few firm convictions on matters of policy and frequently shifts positions to please the people in front of him, making him a frustrating negotiating partner.