If President Obama can stick to his guns, he will win his October standoff with Republicans.

That’s an awfully big “if.”

This president has been consistently inconsistent, predictably unpredictable and reliably erratic. Consider the events of Thursday morning:

Obama gave a rousing speech in suburban Washington, in defense of Obamacare, on the eve of its implementation. “We’re now only five days away from finishing the job,” he told the crowd.

But before he had even left the room, his administration let slip that it was delaying by a month the sign-up for the health-care exchanges for small businesses. It wasn’t a huge deal, but it was enough to trample on the message the president had just delivered.

Throughout his presidency, Obama has had great difficulty delivering a consistent message. Supporters plead for him to take a position — any position — and stick with it. His shifting policy on confronting Syria was the most prominent of his vacillations, but his allies have seen a similar approach to the Guantanamo Bay prison, counterterrorism and climate change. Even on issues such as gun control and immigration where his views have been consistent, Obama has been inconsistent in promoting his message. Allies are reluctant to take risky stands, because they fear that Obama will change his mind and leave them standing alone.

Now come the budget showdowns, which could define the rest of his presidency. Republican leaders are trying to shift the party’s emphasis from the fight over a government shutdown to the fight over the debt-limit increase, where they have more support. A new Bloomberg poll found that Americans, by a 2-to-1 margin, disagree with Obama’s view that Congress should raise the debt limit without any conditions.

But Obama has a path to victory. That poll also found that Americans think lawmakers should stop trying to repeal Obamacare. And that was before House Republicans dramatically overplayed their hand by suggesting that they’ll allow the nation to default if Obama doesn’t agree to their laundry list of demands, including suspending Obamacare, repealing banking reforms, building a new oil pipeline, easing environmental regulations, limiting malpractice lawsuits and restricting access to Medicare.

To beat the Republicans, Obama might follow the example of a Republican, George W. Bush. Whatever you think of what he did, he knew how to get it done: by simplifying his message and repeating it, ad nauseam, until he got the result he was after.

Obama instead tends to give a speech and move along to the next topic. This is why he is forever making “pivots” back to the economy, or to health care. But the way to pressure Congress is to be President One Note.

In the debt-limit fight, Obama already has his note: He will not negotiate over the full faith and credit of the United States. That’s as good a theme as any; it matters less what the message is than that he delivers it consistently.

The idea, White House officials explained to me, is to avoid getting into a back-and-forth over taxes, spending and entitlement programs. “We’re right on the merits, but I don’t think we want to argue on the merits,” one said. “Our argument is not that our argument is better than theirs; it’s that theirs is stupid.”

This is a clean message: Republicans are threatening to tank the economy — through a shutdown or, more likely, through a default on the debt — and Obama isn’t going to negotiate with these hostage-takers.

Happily for Obama, Republicans are helping him to make the case by being publicly belligerent. After this week’s 21-hour speech on the Senate floor by Sen. Ted Cruz (R-Tex.), the publicity-seeking Texan and Sen. Mike Lee (R-Utah) objected to a bipartisan request to move a vote from Friday to Thursday to give House Republicans more time to craft legislation avoiding a shutdown. On the Senate floor, Sen. Bob Corker (R-Tenn.) accused them of objecting because they had sent out e-mails encouraging their supporters to tune in to the vote on Friday. The Post’s Ed O’Keefe caught Cruz “appearing to snicker” as his colleague spoke — more smug teenager than legislator.

Even if his opponents are making things easier for him, Obama still needs to stick to his message. As in Syria, the president has drawn a “red line” by saying he won’t negotiate with those who would put the United States into default. If he retreats, he will embolden his opponents and demoralize his supporters.

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