Cruz is speaking on the Senate floor "until I am no longer able to stand," he said, as a protest intended to prevent Senate Majority Leader Harry ReidHarry Mason ReidMcConnell not yet ready to change rules for Trump nominees The Hill's Morning Report — Sponsored by CVS Health — Trump’s love-hate relationship with the Senate Trump to press GOP on changing Senate rules MORE (D-Nev.) from stripping the bill of the provision that defunds ObamaCare. 

A Paul aide said that the senator, who famously launched a talking filibuster of John Brennan's nomination as CIA director to focus attention on President Obama's policy on drones earlier this year, will join Cruz on the floor to offer "reinforcements" sometime later today. It's unclear how long Paul will talk, or what he's expected to say.

Senate Minority Leader Mitch McConnellAddison (Mitch) Mitchell McConnellSenators introduce bill to overhaul sexual harassment policy The Hill's Morning Report — Sponsored by PhRMA — Republicans see some daylight in midterm polling Exclusive: Bannon says Rosenstein could be fired 'very shortly' MORE (R-Ky.) is opposed to Cruz's gambit.

"Senator McConnell supports the House Republicans' bill and will not vote to block it, since it defunds ObamaCare and funds the government without increasing spending by a penny," McConnell spokesman Don Stewart said Monday in a statement. "He will also vote against any amendment that attempts to add Obamacare funding back into the House Republicans' bill."

Senate Majority Leader Harry Reid (D-Nev.) is expected to advance H.J.Res. 59 with an amendment to remove the House language that defunds ObamaCare.

A vote to end debate on the motion to proceed is expected Wednesday, and Cruz's actions cannot stop that from happening.

— Ramsey Cox contributed reporting.