After his defeats in Texas and Ohio last week, Sen. Barack Obama (Ill.) lost the “Big Mo” in his race for the Democratic presidential nomination. To make matters worse, he’s still got to reckon with the “Big No.”

That would be “the notion,” a nebulous threat Obama has cited with increasing frequency from Capitol Hill to the hustings as the race has heated up.

More specifically, to hear him tell it, he’s been dogged by “the notion that somehow” something might be true, when in his estimation, it clearly is not.

For example, that he is not battle- tested for the general election campaign because of “the notion that somehow the Clintons have coddled me.” Or that Sen. Hillary Rodham Clinton (D-N.Y.) is a better choice because of “the notion that somehow Sen. Clinton is going to be immune from attack.”

Late last month, when Clinton railed against mailers from his campaign in Ohio, Obama responded that “the notion that somehow we are engaging in nefarious tactics, I think, is pretty hard to swallow.”

Of her attack on his health care plan, he said, “The notion that somehow I’m interested in leaving 15 million people without health insurance is simply not true.”

Obama has parried nettlesome notions about his foreign-policy bona fides, such as “the notion that somehow from Washington you get this vast foreign-policy experience,” and his approach to diplomacy, such as “the notion that somehow not talking to countries is punishment to them,” and “the notion that somehow we have had an effective foreign policy by not talking to people.” After all, “the notion that I was somehow going to be inviting them over for tea next week without having initial envoys meet is ridiculous.”

And he has blasted notions suggesting his campaign themes of hope and change mean he’s green or soft, such as, in January, “this notion that somehow being hopeful means you’re naive,” or, back in October, “the notion that somehow changing the tone means simply that we let them say whatever they want to say.”

Some notions are unworkable, such as “the notion that somehow, you know, we’re just going to send [illegal immigrants] somewhere else.” Others are flat-out unconstitutional, such as “the notion that somehow local jurisdictions can’t initiate gun-safety laws to deal with gangbangers and random shootings on the street.”

Obama never uses the lawyerly construction in the soaring stump speeches that have become a hallmark of his campaign. Instead, he relies on the phrase as his go-to in the rhetorical jujitsu of debates and media interviews — a way to acknowledge a challenge while simultaneously deflating it.

“It’s a dismissive,” said Steven Keller, an expert on political oratory at George Washington University’s School of Media and Public Affairs. “‘Notion’ is a way of undermining the legitimacy of the argument — it’s not a claim; it’s not an assertion. It’s a loose, amorphous point. ‘Somehow’ further derogates the point, as though to suggest that there is this absurd argument being made.”

The Obama campaign declined to comment.

Back in January, with Bill Clinton taking a more outspoken role in his wife’s campaign, Obama was fending off dueling notions.

After the former President argued Obama’s Senate votes to fund the Iraq War undercut his initial opposition to it, he responded Jan. 8, saying he was frustrated that Bill Clinton would “continually repeat this notion that somehow I didn’t know where I stood in 2004 about the war.”

The next day, Obama elaborated, saying he had always maintained it was necessary to support the troops once the nation went to war. “So, you know, the notion that somehow that diminishes my clear, unequivocal statements of opposition to the war even before Congress voted to authorize it actually doesn’t make much sense.”

By Jan. 15, he was parrying Sen. Clinton’s suggestion he was responsible for injecting race into the contest. “She is free to explain that, but the notion that somehow this is our doing is ludicrous.”

As he pointed out a week later, “I don’t want us to get drawn into this notion that somehow this is going to be a race that splits along racial lines.”

And on Feb. 4, a day before the Super Tuesday contests, he batted down “this whole notion that somehow Latinos wouldn’t vote for blacks or vice versa.”

Indeed, Obama has been firmly on record criticizing notions for promoting racial divisions, including “the notion that somehow an African-American youth with a book is acting white,” and “the notion that somehow whites won’t vote for African-Americans.” To a conference of black journalists in August, he decried “this notion that somehow if you appeal to white folks, there must be something wrong.”

Capitol Hill has hardly offered the Senator a notional break. Notions followed him to the Senate floor last summer, where during a spat with Sen. Lindsey Graham (R-S.C.) over an amendment Obama had offered to the immigration bill, he had to swat “the notion that somehow that guts … or destroys the bill.” Later, explaining the dispute, he dismissed “the notion that me offering an amendment … that that somehow is not being bipartisan.”

He objected to a Sept. 11 hearing of the Senate Foreign Relations Committee that featured a report on Iraq from Gen. David Petraeus because it “perpetuates this notion that somehow the original decision to go into Iraq was directly related to the attacks on 9/11.”

Back on the campaign trail, notions clouded the debate on the success of the troop surge. In a CNN debate on Nov. 15, Obama said “the notion that somehow because we’ve gone from horrific violence to just intolerable levels of violence, and that somehow justifies George Bush’s strategy is absolutely wrong, and I’m going to bring it to a halt when I’m president of the United States.”

By the Jan. 31 debate, also hosted by CNN, he had softened his tone somewhat, asserting that “the notion that somehow we have succeeded as a consequence of the recent reductions in violence means that we have set the bar so low it’s buried in the sand at this point.”

Obama is not the first politician to wield the phrase. There’s also none other than Vice President Cheney — who Obama jokingly refers to as his cousin because of distant family ties. Advocating for the troop surge in January 2007, Cheney said “the notion that somehow the effort hasn’t been worth it or that we shouldn’t go ahead and complete the task is just dead wrong.”

But Obama has rejected suggestions he rips off other people’s lines. Defending a charge last month from the Clinton campaign he had stolen rhetoric from now-Massachusetts Gov. Deval Patrick (D), Obama said “the notion that I had plagiarized from somebody who was one of my national co-chairs, who gave me the line and suggested that I use it, I think, is silly.”

For all the tough talk about notions, Obama is not averse to having some of his own, though one has come back to haunt him.

After his election to the Senate in 2004, he rejected speculation he would seek the White House, saying, “The notion that somehow I am going to start running for higher office, it just doesn’t make sense.”