Liz Halloran

As investigators combed through evidence in the deadly Boston Marathon bombings, seeking both motive and perpetrator, we turned Tuesday to a security expert for guidance on how the investigation may be unfolding.

Bryan Cunningham, a former CIA officer, assistant U.S. attorney and deputy legal adviser for the National Security Council, served in both the Clinton and George W. Bush administrations. He is now a senior adviser at the consulting firm the Chertoff Group, co-founded by former Homeland Security Director Michael Chertoff.

Rand Paul going to one of the top historically black colleges in the U.S. and trying to school students on who founded the NAACP?

Priceless.

Rand Paul going to one of the top historically black colleges in the U.S. and trying to make a case for his Republican Party as a historic and continuing defender of the civil rights of African-Americans?

Not boring.

And, judging from the reaction the Kentucky senator received Wednesday at Washington's Howard University, less than persuasive.

Thousands of supporters will descend on the U.S. Capitol on Wednesday to call for legislation that creates a path to citizenship for immigrants in the country illegally.

Sound familiar?

But this time, unlike in 2007 and 2010 when immigration legislation died in Congress after similar demonstrations, proponents of an overhaul say politics has swung inexorably toward their side.

"I've been working on this issue for more than a decade, and it feels unstoppable now," says Ana Avendano, director of immigration and community action at the AFL-CIO.

President Obama's campaign for new federal gun control laws takes him to Colorado on Wednesday, and next week back to Connecticut, where the Sandy Hook Elementary School massacre renewed the nation's fraught conversation about guns.

Two county prosecutors fatally shot in Texas. Colorado's top prison official gunned down. And a dozen more members of the U.S. justice community — ranging from police to judges — victims of targeted killings since the beginning of the decade.

What's going on?

The U.S. Supreme Court heard arguments Wednesday in a challenge to the 1996 Defense of Marriage Act, which defines marriage as between "one man and one woman as husband and wife."

It was the court's second and final day of hearing appeals involving same-sex marriage laws. And it served up some memorable observations from the high court denizens.

Justice Ruth Bader Ginsburg characterized same-sex unions under DOMA, which limits federal spousal benefits to heterosexual couples, as the equivalent of "skim milk" marriages.

The U.S. Supreme Court heard lively arguments Tuesday in a challenge to California's Proposition 8 ban on same-sex marriages.

And, as many learned painfully after last year's court decision to uphold Obamacare, it is risky business to predict how justices will rule later based on questions raised in arguments.

So we won't.

Instead, here are five areas of discussion we found interesting, even if they may not prove predictive of the outcome.

It wasn't so long ago that a handful of Vermont legislators in a shabby Statehouse committee room struggled over what to call their proposal to give marriage-like rights to the state's gay and lesbian residents.

Democrat Howard Dean, governor at the time, had already made clear he'd veto any legislation labeled "marriage." Suggestions like "domestic partner relationship" were too clunky; "civil accord," they decided, evoked a car model.

Republican Sen. Rand Paul of Kentucky doubled down Tuesday on a previous call for a path to citizenship, telling a major Hispanic business group that his message to the nation's illegal immigrants is: "If you wish to live and work in America, then we will find a place for you."

Conservatives, he told the U.S. Hispanic Chamber of Commerce, must "become part of the solution" to immigration, including dealing with the estimated 11 million illegal immigrants now living in the U.S. In his Washington speech, Paul said:

It is a theme that has become increasingly familiar during the rapid evolution of American political attitudes toward same-sex marriage: People who learn that a friend or loved one is gay are far more likely to support same-sex marriage, even if they were once adamantly opposed.

Ohio Sen. Rob Portman, who became the first Republican in the U.S. Senate to openly endorse same-sex marriage, is simply the latest.

Leaders of the Roman Catholic Church made history twice Wednesday, electing the first pope from the Southern Hemisphere and the first Jesuit.

In choosing 76-year-old Cardinal Jorge Maria Bergoglio of Argentina, now Pope Francis, the College of Cardinals signaled the growing importance of Latin America, Africa and Asia in the church's fortunes.

But they also affirmed their commitment to traditional church doctrine.

The nation has twice elected an African-American president.

Black voters have been turning out for general elections in rates that for the first time in U.S. history rival those of whites.

Edward Blum isn't a lawyer, and he doesn't play one on TV.

But he has been the driving force behind two race-related cases before the U.S. Supreme Court this term, including one that justices will hear Wednesday that seeks to roll back a key section of the 1965 Voting Rights Act.

The other, Fisher v. University of Texas, which challenges the use of race and ethnicity in public college and university admissions policies, was heard by the court in October and awaits its decision.

A worldwide Catholic conversation that many church-watchers say effectively stopped when Benedict XVI was elected pope eight years ago has been rekindled by his announced plan to resign at month's end.

Celibacy. Women's roles. Same-sex marriage. Clergy sexual abuse revelations.

And, perhaps most significantly, the spectacular growth of the church in the more religiously conservative "global south" — Latin America, Africa and Asia — while its fortunes continue to decline in the increasingly secular West.