Sen. Chuck Grassley (R-IA) (2nd L) speaks as (L-R) Sens. Tom Cotton (R-AR), Joni Ernst (R-IA), David Perdue (R-GA) and Thom Tillis (R-NC) listen during a news conference on immigration February 12, 2018 at the Capitol in Washington, DC.

A Republican senator asserted Tuesday that President Donald Trump's immigration plan is the only measure that could pass Congress.

Sen. Tom Cotton of Arkansas spoke as the Senate was scheduled to start an open debate on how to proceed.

Bipartisan senators will continue contentious discussions on the best measure to protect up to 1.8 million young immigrants brought to the United States illegally as children and boost border security. A measure drafted by GOP senators including Cotton aims to mirror Trump's immigration proposal, which calls for restrictions on legal immigration that Democrats consider unacceptable.

"The president's framework bill is not an opening bid for negotiations. It's a best and final offer," Cotton told "Fox and Friends" on Tuesday morning.

The Senate will have an open process this week to propose amendments to include in an immigration bill. Measures will need 60 votes to pass. If all 51 Republican senators support Trump's framework, they will need nine Democrats to pass it.

Lawmakers are seeking legislation to enshrine protections for the young immigrants who were protected or eligible for the Obama-era Deferred Action for Childhood Arrivals. Trump ended DACA in September with a six-month delay.