President Donald Trump urged conservative activists on Tuesday night to help lobby Senators in favor of a GOP tax reform package, as despite some infighting, Republicans seemed like they would be able to approve a budget outline this week in the Senate, a plan which would allow for future legislative action on a tax bill - without the threat of a Senate filibuster.

"Let's give our country the best Christmas present of all - massive tax relief," the President said in a speech at the Heritage Foundation, where his vow of big tax cuts drew large cheers from the audience.

"This is our once-in-a-generation opportunity to revive our economy," Mr. Trump added, though he acknowledged that he doesn't expect much support from Democrats in the Congress.

Before any tax bill can be brought up on the floor of the House and Senate, both chambers must approve a budget outline for 2018, which authorizes the use of the 'budget reconciliation' process for tax reform - helping the GOP to avoid a Senate filibuster. That was the same legislative tool used in a failed bid to overhaul the Obama health law.

In an important sign for the White House, Sen. Thad Cochran (R-MS) - who had been absent for weeks with an illness, returned to Capitol Hill on Tuesday - and then, GOP leaders won the support of another key Republican Senator, who has tangled repeatedly with the President.

"I support the Senate budget resolution because it provides a path forward on tax reform," said Sen. John McCain (R-AZ), who still wants GOP leaders to add more money to the budget outline for military needs.

Still not ready to commit to the budget or tax plans was Sen. Rand Paul (R-KY), who lobbed a series of pointed jabs at both McCain, and Sen. Lindsey Graham (R-SC), accusing them of trying to use budget gimmicks to funnel more money to the Pentagon, instead of finding ways to restrain spending.

In a first test vote, the Senate voted 50-47 in favor of beginning debate on the budget framework for 2018, which would balance the budget by 2026. A House budget outline would achieve that a year later.

No Democrats joined with Republicans to begin the Senate debate, as right now, the White House faces a difficult task in getting any Democratic lawmakers to endorse the President's budget or tax plans.

"It's going to be hard to get the Democrats, because they're obstructionists, and they vote in blocks," the President said in his Tuesday night speech.

If no Democrats cross party lines on taxes, that makes it all the more important for the GOP to stick together in the Senate, or the GOP could face the same outcome as on health care reform.

No legislative language for a tax reform plan has been released as yet by the GOP. Lawmakers don't expect to see all the details until next month.