The top Senate Democrat on Sunday predicted that Congress will pass and send to President Barack Obama legislation overhauling the U.S. immigration system, saying "things are looking really good."
Obama last week expressed hope Congress can get a deal done on immigration, possibly in the first half of the year.
The president is proposing to give the roughly 11 million U.S. illegal immigrants - most of whom are Hispanics - a pathway to citizenship, a step that many Republicans have long fought.
Obama's fellow Democrats control the Senate, but Republicans control the House of Representatives.
Appearing on the ABC program "This Week," Reid was asked whether immigration legislation can win House passage.
"Well, it's certainly going to pass the Senate. And it would be a bad day for our country and a bad day for the Republican Party if they continue standing in the way of this. So the answer is yes," Reid said.
Obama choose Reid's home state of Nevada, with a sizable Hispanic population, as the site for a major speech last Tuesday pushing Congress to pass an immigration bill.
Hispanic voters were crucial in helping Obama beat Republican nominee Mitt Romney - who advocated "self-deportation" of illegal immigrants - in Nevada in November.
"It has to get done," Reid said of immigration legislation.
"It's really easy to write principles. To write legislation is much harder. And once we write the legislation, then you have to get it passed. But I think things are looking really good," Reid added.
After years on the back burner, immigration reform has suddenly looked possible as Republicans, chastened by the fact that more than 70 percent of Hispanic voters backed Obama in the November election, appear more willing to accept an overhaul.
Obama has pushed for a pathway to citizenship for illegal immigrants already in the United States that is faster than one proposed by a bipartisan group of eight influential senators.
Rather than emphasize border security first, Obama would let illegal immigrants get on a path to citizenship if they undergo national security and criminal background checks, pay penalties, learn English and get in line behind those foreigners seeking to immigrate legally.
The bipartisan Senate plan envisions taking steps to toughen security along the U.S.-Mexican border before setting in motion the steps illegal immigrants must take to gain legal status.
"Every time I've talked about this, I say there are a few things we need," Reid said. "Number one is border security, southern and northern border security. We have to do that. We have to have a pathway to legalization. We have to make sure that the employer sanctions work."
On another matter, Reid expressed "utmost confidence" in New Jersey Democratic Senator Bob Menendez, incoming chairman of the powerful Senate Foreign Relations Committee who last week denied allegations that he had engaged in sex with prostitutes during free trips to the Dominican Republic provided by a political donor.
"Oh, I have confidence he did nothing wrong, but that's what investigations are all about," Reid said.
Menendez is one of the members of the bipartisan Senate group working on immigration.