Sen. Marco Rubio (R-FL) called on President Donald Trump on Tuesday to clarify what kind of legislation he would sign to protect young undocumented immigrants from deportation.

Attorney General Jeff Sessions announced earlier in the day that Trump had rescinded DACA, or Deferred Action for Childhood Arrivals, which protects nearly 800,000 young undocumented people from deportation. The first deportations of DACA recipients could begin in as little as six months.

Trump said in a statement following Sessions’ announcement: “Congress now has the opportunity to advance responsible immigration reform that puts American jobs and American security first.”

Rubio, in a statement, called on Trump to clarify what he was willing to sign into law.

“It is important that the White House clearly outline what kind of legislation the president is willing to sign,” he wrote. “We have no time to waste on ideas that do not have the votes to pass or that the president won’t sign.”

Rubio also wrote that he had “long supported accommodating those brought to this country illegally through no fault of their own.”

“However,” he added, “I have always felt that President Obama’s executive action was unconstitutional and that the right way to address this issue was through legislation.”

In 2013, Rubio co-authored the so-called “Gang of Eight”’s immigration bill, which included a lengthy path to citizenship for some undocumented immigrants. During the 2016 presidential campaign, however, he distanced himself from the effort.