President Donald Trump goes to Capitol Hill today to attend a Senate Republican policy lunch for the first time, his visit coming as lawmakers begin to grapple with the details of a tax reform package, as some Republicans indicated they wanted to see Mr. Trump set out more of what he wants accomplished on taxes, health care, and other key issues.

“What are his non-negotiables?” asked Sen. James Lankford (R-OK), who told reporters it’s time for the President to deliver more specifics on what he likes – and doesn’t like – when it comes to the fine print of tax reform.

“We’ve got big issues that are moving – those have to be resolved – and at least know where the President’s priorities are,” Lankford added in an interview just off the Senate floor.

Some GOP Senators didn’t see much coming out of the lunch meeting – Sen. Bob Corker (R-TN), who has sparred often with the President in recent weeks – said it would be nothing but a ‘photo op’ – and that set off another round of Twitter volleys.

It’s the first time Mr. Trump will be in the same room as Corker since their recent spat, where the President labeled the Tennessee Republican, “Liddle’ Bob Corker” in a tweet.

And this morning, the President fired off another jab at Corker, just hours before the GOP lunch – and Corker fired right back.

The visit by the President comes at an important time legislatively, as GOP lawmakers in the House and Senate are ready to cobble together the details of a tax reform package.

While Republican lawmakers talked optimistically on Monday about unveiling the full details of a tax plan as early as next week, there were reports that the details weren’t even finalized.

The first stop for tax reform will be the House Ways and Means Committee, chaired by Rep. Kevin Brady (R-TX), who told reporters on Monday that he’s optimistic the Congress will be able to move quickly on the plan.

White House officials have repeatedly said that the average American family will see a benefit of around $4,000 from tax reform.

“If that’s true it will be awesome, if it’s not true, heads will roll,” said Rep. Ted Yoho (R-FL).

“I just hope we can get it through,” Yoho added.