(CNN) -- The Republican 2016 presidential field is starting to come into focus with potential contenders making notable moves this week.
Here's a breakdown of the latest headlines starting to shape the early race for the Republican nomination.
Portman is out
Pollsters can cross one name off their long list: Rob Portman. The Ohio Republican announced Tuesday he's running for re-election to his Senate seat.
Portman was vetted, but ultimately not picked, to be Mitt Romney's running mate in 2012, and he would have been the first pro-same sex marriage Republican presidential candidate if he ran this cycle.
He said as recently as two weeks ago that he was considering a presidential run, telling CNN's Erin McPike that he "probably (has) more experience than other people who are running or thinking about running."
Instead the senator will seek a second term in the Senate, where he thinks he can "play the most constructive role."
Bush is "thinking"
Jeb Bush reiterated that he's still considering a presidential run, revealing more details Monday about his decision-making process.
"I'm thinking about running for president, and I'll make up my mind in short order," the former Florida governor said at an event hosted by the Wall Street Journal.
He said he's determining whether his candidacy could "lift people's spirits and not get sucked into the vortex," adding that he's also questioning if "the sacrifice for my family is tolerable."
With Bush considered a potential frontrunner, the rest of the GOP field is eagerly awaiting his decision. Those perhaps most interested include Sen. Marco Rubio of Florida, who was mentored by Bush, and other candidates who appeal to moderate Republicans, like Gov. Chris Christie of New Jersey.
"I don't know if I'd be a good candidate or a bad one," Bush said. "I kind of know how a Republican can win."
Ben Carson on the verge of becoming a political phenomenon
A renowned neurosurgeon who's become popular in conservative circles, Ben Carson is still climbing up the charts, according to a new CNN/ORC International Poll. Carson came in second place behind Mitt Romney in the survey, which measure support for potential 2016 contenders.
Carson rose to political fame after publicly chiding the direction the country was going during his remarks at the National Prayer Breakfast in February 2013. President Barack Obama was sitting just a few feet away.
Since then, he's been likened to a rockstar among conservatives, and he's become the only African-American Republican expressing interest in a 2016 presidential run. His abhorrence for political correctness has also made him a favorite among radio talk shows.
"I try to talk about what I actually see that's going on and this is what we need in America," he told CNN's Mark Preston for a profile piece. "We need people who are not afraid to express themselves and who are not afraid to debate issues."
In the interview, Carson said that if the right candidate emerges before May 1, he won't run for the White House.
Rand Paul is definitely running in 2016 ... for the Senate
While Sen. Rand Paul has been saying for more than a year that he plans on running for a second term in the Senate, the Kentucky Republican made it official Tuesday.
But he has a bumpy road ahead. Kentucky election law allows candidates to appear on a ballot only once at a time, making it difficult for Paul if he also runs for president — a decision he told the Lexington Herald-Leader that he's about "four to six months" away from making.
His allies in the state Senate tried to help him by passing a bill that tweaks the law, but the measure stalled in the Democratic-controlled state House.
Still, Paul has other options, including a possible court challenge or convincing the state GOP to change its nominating system in 2016 from a primary to a caucus. That way, his name wouldn't appear on a ballot. Or, he could just not appear on the ballot at all and forego Kentucky's delegates.
It's unclear which direction he'll take, but expect Democrats to seize on Paul's attempt to run for two offices.
"Where I come from, people think if you can't make up your mind on which office you want to run for, then you ain't fit to serve in either one," Kentucky House Speaker Greg Stumbo told CNN.
Chris Christie wins high praise from Iowa's top Republican
In a bizarre 2016 storyline, Gov. Chris Christie vetoed a popular bill that would have banned gestation crates that severely limit the mobility of pigs in New Jersey.
While his decision drew strong pushback from animal rights activists and other supporters, the veto kept Christie in high standing with Gov. Terry Branstad of Iowa. The Hawkeye State is the nation's top pork producer.
Branstad, who holds significant influence in Iowa's first-in-the-nation presidential nominating contest, said Monday that Christie's veto was a "good decision," adding that he personally lobbied Christie to reject the bill.
Christie said he vetoed the bill because it was a "solution in search of a problem" and a "political movement masquerading as substantive policy."
But his opponents say the decision was simply a political ploy with 2016 ambitions on his mind. Democratic state Sen. Ray Lesniak, a strong backer of the bill, pledged that the state legislature would attempt to override the veto, according to NJ.com.
Mitt Romney's hair. Enough said.
One can hardly write about 2016 without mentioning Romney and the latest earth-shattering news that his picture perfect hair is -- wait for it -- not always perfectly coiffed.
The bombshell was revealed by his wife, Ann Romney, on Twitter during Thanksgiving weekend.
Disheveled or not, he's still the most favored potential Republican contender, carrying 20% support among Republican voters in CNN's latest poll, with other names getting 10% or less.
He may have said a thousand times in the past two years that he's not running again, but until someone else emerges as a frontrunner, voters are poised to keep him as their top choice.
Oh, right. And Newt Gingrich said this.
Talking about the emerging field, former House Speaker Newt Gingrich, who ran for president in 2012, didn't rule out the idea of another run.
"I haven't totally closed the door, but I'm certainly not opening it," he said Tuesday on CNN's "Wolf."
He later added that it's actually "very implausible" and that he "doubts very much" he'll "end up in that game."
"But that tells you how early it is," he said.
CNN's Jeremy Diamond, Dana Bash, Eric Bradner, and Mark Preston contributed to this report.