By MICHAEL FALCONE ( @michaelpfalcone )

NOTABLES

• RUBIO CALLS RAND PAUL 'CHIEF CHEERLEADER' OF OBAMA FOREIGN POLICY: Sen. Marco Rubio responded to criticism from fellow Republican and potential 2016 presidential rival Sen. Rand Paul over his position on Cuba, insisting that he would oppose the "Obama-Paul foreign policy," and referring to the Kentucky senator as "chief cheerleader" of the president's overseas agenda. "Rand, if he wants to become the chief cheerleader of Obama's foreign policy, he certainly has a right to do that," Rubio, R-Florida, told ABC's GEORGE STEPHANOPOULOS on "This Week." "I'm going to continue to oppose the Obama-Paul foreign policy on Cuba because I know it won't lead to freedom and liberty for the Cuban people, which is my sole interest here." Earlier this week, Paul tweeted on Rubio's position on engagement with Cuba that he "is acting like an isolationist who wants to retreat to our borders and perhaps build a moat. I reject this isolationism." http://abcn.ws/1wSpO2j TRANSCRIPT: http://abcn.ws/13KrD6R

• RAND RESPONDED: With a tweet: " @SenRandPaul: . @marcorubio forgot to mention his support for Obama's funding of Musl. Brotherhood, arming Islamic rebels, and Hillary's war in Libya." And following Rubio's appearance on "This Week," Doug Stafford, senior advisor to Paul, in a statement to ABC News, said that "With all due respect, Senator Marco Rubio was captain of the GOP cheerleading team for Obama's arming of Syrian rebels, bombing Libya resulting in a jihadist wonderland, and illegally giving foreign aid to Egypt's military government. The Rubio-Obama foreign policy has made the Middle East and North Africa less safe."

• ANALYSIS - ABC's RICK KLEIN: Early bets on who will be the least popular person on the 2016 Republican debate stage? The shortest odds are on Sen. Rand Paul, who broke an unwritten rule of intra-caucus social-media behavior by launching a series of Twitter attacks on Sen. Marco Rubio late last week, on Cuba policy. That included a loaded labeling by Paul, who said that Rubio is being an "isolationist." Paul is making clear, again, that he'll be an aggressive and sometimes unpredictable force in the 2016 campaign. He will, of course, be making intriguing arguments that might confuse the GOP field as much as it clarifies voters' choices. For his part, Rubio found a response: "Rand - if he wants to become the chief cheerleader of Obama's foreign policy, he certainly has a right to do that," Rubio told George Stephanopoulos Sunday on ABC's "This Week."

POLLING REPORT - CLINTON: OFF HER PEAK, BUT STILL TOWERING. Hillary Clinton is off her peak but still overwhelmingly strong in support for the Democratic presidential nomination in 2016, while Elizabeth Warren has inched up in the latest ABC News-Washington Post poll. ABC's GARY LANGER notes, Clinton's backed by 61 percent of Democratic and Democratic leaning independents who are registered to vote, giving her a vast advantage over potential rivals Joe Biden, at 14 percent, and Warren, the freshman U.S. senator from Massachusetts, at 13 percent. http://abcn.ws/1wS7xCd

-CLINTON'S SUPPORT HAS SLIPPED from 69 percent in June, down by 8 points, while support for Warren is up by 6 points - not remotely enough to make it look competitive at this stage, but movement nonetheless, LANGER notes. Biden has held essentially steady. Warren's been described as the darling of liberals, and indeed her support among liberals has gained 11 points since June, while Clinton's has slipped in this group by 14 points. Nonetheless, Clinton still holds a wide 59-19 percent lead over Warren among liberals, with 12 percent for Biden. (Narrow it down to "very" liberals, combining the last two ABC-Post polls for an adequate sample size, and it's similar - Clinton 63 percent, Warren 21, Biden 6.) http://abcn.ws/1wS7xCd

2016 PREVIEW - RUBIO SAYS HE HAS 'TREMENDOUS RESPECT' FOR JEB BUSH. Asked about the race for the White House in 2016, Sen. Marco Rubio, R-Florida, said Sunday on "This Week" that he anticipated supporting whomever the Republican party nominates, while seeming to indicate that Paul, whom he had just discussed, did not fit the bill, reports ABC's BENJAMIN BELL. "I'm pretty confident that the Republican nominee for president will be someone who has a pretty forceful role - view of America's role in the world as a defender of democracy and of freedom and also understands that it's important for America to be engaged on the global stage," he said. When asked about former Florida Gov. Jeb Bush's potential entrance into the 2016 race, Rubio said he had "tremendous respect" for Bush and said he would be a very "credible" and "strong" candidate if he decides to run. Rubio told Stephanopoulos he has not decided whether to make his own bid for the presidency. "I think ultimately, that first I have to make the decision that that's what I want to do, that that's the best place for me to serve the country at this time. And then I think that's why you have a primary. And that's the greatness about our system of government in comparison to what they have in Cuba, for example, where they don't get to choose their leaders," he said. http://abcn.ws/1wSpO2j TRANSCRIPT: http://abcn.ws/13KrD6R

WHAT WE'RE WATCHING - 'THIS WEEK' ROUNDTABLE: JEB BUSH INCHES CLOSER TO 2016. ABC's JONATHAN KARL and the "This Week" roundtable weigh in on the impact of Jeb Bush's move toward entering the 2016 race, and how the GOP field is shaping up. WATCH: http://abcn.ws/1zLk2zm And the roundtable also debated President Obama's latest move on Cuba and his lame duck agenda, and the response to the shooting of two NYPD officers. WATCH: http://abcn.ws/1sNfS57

OBAMA IN HAWAII - AN INSIDE LOOK AT THE FIRST FAMILY'S WINTER VACATION. It's been a long year for President Obama (see: ISIS, Ebola, Democrats' staggering loss in the 2014 midterms) - and the commander-in-chief is in serious need of a little R&R. On Friday, Dec. 19, he departed for a 16-day holiday in his native state, Hawaii. It's the family's sixth Oahu vacation since the president took office. ABC NEWS is along for the ride, and we're giving you a behind-the-scenes look at what it's like on an Obama vacay. http://abcn.ws/1AmVKgt

WHO'S TWEETING?

@guycecil: I'm #ReadyForHillary & looking fwd to helping however I can but eager to serve in other ways & explore other paths http://www.politico.com/story/2014/12/guy-cecil-hillary-clinton-113731.html …

@bethreinhard: . Hide your donors 2016ers, @JebBush has already been to Miami, Dallas, Chicago http://www.wsj.com/articles/jeb-bushs-ties-to-donors-put-rivals-in-a-bind-1419208983 …

@tripgabriel: One sign Ben Carson moving toward GOP candidacy: he has spoken to comms experts on toning down outrageous statements http://www.nytimes.com/2014/12/22/us/politics/gop-hopes-for-unity-may-be-upset-by-ben-carson.html?ref=politics …

@bykowicz: The 'I Can't Breathe' Profiteers @llerer notes there's a super-PAC and trademark petition. http://www.bloomberg.com/politics/articles/2014-12-21/the-i-cant-breathe-profiteers … via @bpolitics

@jdelreal: Jon Huntsman Sr.: "All I can say is Mike Lee is an embarrassment to the state of Utah." http://www.politico.com/story/2014/12/mike-lee-tea-party-2016-elections-113730.html#ixzz3MdKP7jlI …