Secretary of State John Kerry is on a roll, notching major foreign policy victories for President Obama including, most recently, a tentative deal to curb Iran's nuclear ambitions.

That's great news for the beleaguered White House and for Kerry's own legacy. Yet in racking up so many prominent successes, Kerry is inadvertently overshadowing the accomplishments of his predecessor, Hillary Clinton, and potentially weakening her case for a 2016 bid.

Since taking over at the State Department in February, Kerry struck a deal, via Russia, to eliminate Syria's chemical weapons (and avert a possible U.S.-led military strike); convinced Israel and Palestine to hold peace talks; and secured an interim agreement with Iran to ease some sanctions in exchange for a freeze on parts of its nuclear program. On Iran in particular, Kerry played a central role, having forged ties in 2011 with Oman that paved the way for the final agreement.

Given all that success, Kerry has in one year "rolled up more tangible accomplishments than his celebrated and cautious predecessor, Hillary Clinton, did in four," says Bloomberg's Albert R. Hunt.

Clinton, for her part, wasn't a dud of a secretary either. But her accomplishments are more intangible — promoting education and women's rights — than Kerry's landmark peace achievements.

As a result, "some people close to Mrs. Clinton worry that, because of the high profile given to her work for women's rights, and the headlines now being generated by the hyperkinetic Mr. Kerry, her efforts on trickier diplomatic situations have been eclipsed," says The New York Times.

If Clinton's accomplishments are indeed eclipsed, it could undercut part of her résumé come 2016. She was enormously popular while in the State Department — her favorability rating topped out around 66 percent at one point — but has since slipped as she's moved further from her old job.

Part of that slide is thanks to Republican efforts to paint Clinton as a feckless figurehead with a dubious record, and to define her tenure in one word: Benghazi. Republicans over the summer held purported whistle-blower hearings into the Libyan embassy attack, with a clear subtext blaming Clinton for whatever failures led to the deaths of four Americans.

Thus, on the right, Clinton's tenure is remembered for her "unwillingness to take risks, unwillingness to lead, willingness to stab a lot of people in the back. And dead people," says Danielle Pletka of the conservative American Enterprise's Institute.

Then again, Clinton's muted reign was likely by choice. As Bill Scher wrote recently in The Week:

The former secretary is a presidential aspirant. The current secretary is a presidential also-ran.

Clinton would be risking her last chance at moving to 1600 Pennsylvania Ave. if she crashed and burned at Foggy Bottom (hence the desperate attempts by the Republican Party to manufacture a scandal out of the Benghazi attack). But Kerry has nothing to lose and everything to gain by aggressively pursuing every diplomatic Holy Grail in sight. For him, secretary of state is the career capstone, not a stepping-stone." [The Week]

In that light, a lower-key run at the State Department could be more desirable for Clinton's believed endgame, even when followed by the relative bombast of Kerry's whirlwind efforts. And if Kerry is indeed accidentally stepping on Clinton's toes, he's nonetheless still hyping her credentials. At a November event he hailed her as one of the nation's "remarkable secretaries of state," adding that "nobody has done more to advance the cause of women."

Clinton also has a memoir due out next year that will recast her career and resurface forgotten achievements, and she's already traveling the country for speaking gigs. Meaning, there is plenty of opportunity for her to remind everyone what she did before Kerry took the reins.

Plus, Clinton remains incredibly popular despite her year-long slide in opinion polls, and even some leading Republicans are unafraid to praise her in public as an "outstanding" secretary of state.

Kerry may be making Clinton's State Department résumé look less impressive now, but it will take much more than a successful successor to significantly undercut Clinton's presidential ambitions down the road.