NEW YORK -- President Obama on Friday continued to denounce voter apathy in a push to get more Democrats to the polls for midterm elections, and blasted Republicans for passing laws he said makes it harder to vote.

Addressing the annual convention of the National Action Network, a nonprofit group founded by the Rev. Al Sharpton, Obama said people need to put aside distrust of and frustration with politics and get to the polls.

"The number of people who voluntarily don’t vote dwarfs" whatever "laws that are put in place to diminish the voting rolls" might do, Obama told a cheering, fired-up crowd of 1,600 at a Manhattan hotel. "We can’t use cynicism as an excuse not to participate."

Obama also continued hammering a theme he first raised at a Houston fundraiser this week: that Republicans are actively trying to keep people away from the polls.

“This recent effort to restrict the vote has not been led by both parties. It’s been led by the Republican Party,” Obama said. "If your strategy depends on having fewer people showing up to vote, that’s not a sign of strength. That’s a sign of weakness. And not only it is ultimately bad politics, ultimately it is bad for the country."

A day after speaking at a commemoration of the 50th anniversary of the Civil Rights Act at the Lyndon B. Johnson Presidential Library in Texas, Obama said the right to vote is threatened in a way today that it has not been since the act was signed into law by Johnson.

He blasted efforts to make voters produce identification cards, saying that about 60 percent of Americans don't have passports.

"Just because you don’t have the money to travel abroad doesn’t mean you shouldn’t be able  to vote here at home," he said.

Obama's focus on voting rights is part of a broad Democratic strategy to boost turnout for the midterms, which strategists have identified as the best, and perhaps only,way for the party to make gains in the House and retain the Senate. In 2012, 42 percent of eligible voters didn't vote, according to the United States Elections Project, up from 38 percent in 2008. However, African American turnout was up sharply in 2008 and 2012, surpassing whiter turnout for the first time, and Obama's appearance at the Sharpton event was geared toward sustaining that trend for the midterms.

After making his case, Obama brought up an issue that most thought he'd rather forget -- the controversy over his birth certificate.

"And just to be clear, I know where my birth certificate is,” Obama said to applause. “You remember that? That was crazy. I haven’t thought about that in awhile."

Obama also invoked the memory of three civil rights workers who were killed in Mississippi in 1964 while fighting for equal voting rights.

"The least you can do is take them up on the gift they have given you," Obama said to a standing, clapping crowd. "Go out there and vote. You can make a change. You do have the power."

At a time when Democrats are starting to embrace Johnson, a complicated man with a complicated legacy, Obama recalled his visit Thursday to the Johnson presidential library. Like his speech there, the nation's first black president used starkly personal language to connect himself to the legacy of the civil rights movement.

"Standing there, I thought of all the Americans known and unknown who made it possible for me to stand in that spot, who marched and organized and sat in and stood up for jobs, and for justice," Obama said.

The gains made from the Civil Rights Act have happened concurrent with his life, said Obama, who is 52 years old. "To see the progress that has been made is to see my life.”

Obama spoke of the legacy of Johnson's Great Society, including Medicare and Social Security. He connected them to the progress that he said his administration has made despite the economic downturn, including health-care reform.

Republican governors who are not allowing Medicaid expansion in their states "aren't doing the right thing," Obama said.

"We have states who just out of political spite are leaving millions of people uninsured who could be getting health insurance right now. No good reason for it," he said. "If you ask them ‘what’s the explanation?’ they can’t really tell you.”

But the speech wasn't all serious. Sharpton introduced Obama as the "action president," but Obama said there's more to him than that.

"I do also have style," he said.

And the best part about not being able to run for a third term? He won't have to get another dog.

"Three dogs is too many," he said.