Rep. Luis Gutierrez (D-Ill.), a key player in the immigration debate, photographed outside the Capitol on Oct. 11, 2013. (Bill O'Leary/The Washington Post)

Leading proponents of immigration reform are preparing to throw their full political weight behind President Obama as he prepares to use executive authorities to revamp the nation's immigration laws.

Reps. Zoe Lofgren (D-Calif.) and Luis Gutierrez (D-Ill.), two of the most vocal proponents for immigration reform, began circulating a letter of support on Wednesday that lays out the economic, political and legal arguments that they hope Obama's allies will be making on his behalf once he takes action and begins facing Republican criticism for doing so.

A draft of the letter is being circulated among Democrats with plans to formally send a copy to the White House later Wednesday or on Thursday. The Washington Post obtained a copy of the draft from a congressional aide. The offices of Lofgren and Gutierrez didn't immediately respond to requests for comment.

Obama said last week that he is planning to use his executive powers to overhaul at least part of the nation's immigration system, dismissing calls by Republican congressional leaders that he delay doing so. Obama is said to be considering a suite of options that could grant temporary legal status to as many as 5 million illegal immigrants, according to several people familiar with his plans. He is expected to act once he returns from his current trip to Asia and Australia and before the end of the year.

In the letter, Democrats tell Obama they "were very disappointed" when he postponed taking action before the midterm elections, but are encouraged that he still plans to do so soon.

"We hope that your actions will prevent the separation of undocumented family members of U.S. citizens, lawful permanent residents, and DACA beneficiaries and offer protection to others who have long worked in the United States and have established strong ties with our communities. We further hope that they will make our immigration enforcement efforts more sensible and humane," they write.

"Bold and meaningful executive action will provide a boost to our national and local economies," they add later. And they believe that Obama's legal authority to act "is clear and substantial."

They cite the 2012 U.S. Supreme Court case, Arizona v. United States, where Chief Justice John Roberts wrote that the Obama administration retains "broad discretion" to decide "whether it makes sense to pursue removal [of illegal immigrants] at all."

They add that "every past President, starting from President Dwight D. Eisenhower more than half a century ago, has used such authority when dealing with similar issues regarding the national interest."

As for the political fallout, Democrats believe Obama is correct to blame Republicans for congressional delay: "For the past two years it was not Senate Democrats that blocked much-needed legislation, it was House Republicans. That obstacle to sensible immigration reform still remains. Let us also not forget that congressional Republicans previously blocked reform in 2006 and 2007."

In addition to this letter, Democrats are also preparing to hold a series of public events in the coming days to continue building the case for Obama’s executive actions.

Members of the Congressional Hispanic Caucus rallied on Wednesday afternoon with members of the military who have benefited from immigration policies that allowed them to become U.S. citizens. And several Democrats plan to begin making floor speeches in support of Obama starting on Thursday, according to aides.

Here's a full copy of the draft letter:

Dear Mr. President:

It is extremely frustrating that Republican leaders in the House refused to allow a vote on the bipartisan immigration reform bill the Senate passed last year. Even today, if Republican leaders allowed a vote, the bill would pass. But they won’t.

When Republicans blocked legislation, your pledge to use Presidential power under existing law to improve our immigration system gave us hope. Without such changes, our economy will continue to suffer and families in our communities will continue to be torn apart.

Although we were very disappointed when you postponed action until after the November election, we were encouraged last week when you reaffirmed your promise to act before the end of the year.

We hope that your actions will prevent the separation of undocumented family members of U.S. citizens, lawful permanent residents, and DACA beneficiaries and offer protection to others who have long worked in the United States and have established strong ties with our communities. We further hope that they will make our immigration enforcement efforts more sensible and humane.

Bold and meaningful executive action will provide a boost to our national and local economies. It will strengthen communities and promote family unity. It will help the government focus limited enforcement resources on those who pose a true danger to the public. And by providing an opportunity for millions of undocumented immigrants to register with the government—provide detailed biographic information, undergo criminal background checks, demonstrate continuing compliance with tax laws—it will protect American and immigrant workers alike by reducing the threat of exploitation and abuse.

The legal authority for taking executive action is clear and substantial. Just two years ago, the Supreme Court under Justice John Roberts reaffirmed that the administration retains “broad discretion” to decide “whether it makes sense to pursue removal at all.” Arizona v. United States, 132 S.Ct. 2492, 2499 (2012). And executive action in this area is anything by unprecedented. In fact, every past President, starting from President Dwight D. Eisenhower more than half a century ago, has used such authority when dealing with similar issues regarding the national interest.

Like us, you have heard Republicans warn that any actions you take will “poison the well” and prevent them using their upcoming majority in the Senate to address our broken immigration system. However, for the past two years it was not Senate Democrats that blocked much-needed legislation, it was House Republicans. That obstacle to sensible immigration reform still remains. Let us also not forget that congressional Republicans previously blocked reform in 2006 and 2007.

As you said last week, “What we can’t do is just keep on waiting. There’s a cost for waiting.” That cost is measured in the tens of thousands of parents of U.S. citizen children who are deported each year. It is measured in the emotional price children and DACA recipients pay worrying about whether their parents will come home at the end of the day. Our national security suffers whenever we spend precious enforcement resources on hardworking immigrant families, rather than on criminals and those who mean our communities harm.  And American workers’ wages and working conditions are consistently undermined as long as millions of immigrant workers are working in the shadows and off the books. We agree with you, Mr. President. We can no longer afford to wait.

As you have said, it is ultimately the job of Congress to reform our broken immigration system by enacting legislation. But by failing to do their job—and repeatedly interfering with your efforts to do your job—congressional Republicans threaten to take our immigration system hostage and preserve a status quo that everyone agrees is unacceptable. Their failure to act must not inhibit your commitment to governing.

We will stand with you as you take bold and meaningful action, consistent with existing law and historical precedent, to protect American families, strengthen local communities and grow the economy.