Trump rallies support for 'once in a lifetime' tax overhaul opportunity

Before an expected Senate vote, the president said a "moment of truth" awaits.

"Our focus is on helping the folks who work in the mailrooms and machine shops of America, the plumbers and the carpenters, the cops and the teachers, the truck drivers and the pipe fitters … all of the people who give their best each and every day to take care of their family and the country they love," he said.

"This week's vote can be the beginning of the next great chapter for the American worker," Trump added.

Democrats have decried the plan as one that unduly benefits upper-class taxpayers and increases the federal deficit at the expense of economic benefits for those middle- and lower-income citizens cited by Trump on Wednesday. All 48 Democratic and independent senators are expected to oppose the bill, in a vote that could come as early as Thursday. Trump has labeled their efforts as "obstruction."

In light of the bill's lack of bipartisan support, he appeared to issue a warning Wednesday to the Republicans still determining their position on the matter.

"Now comes the moment of truth," he said.

ABC News' Alexander Mallin contributed to this report.