Brexit deal a much-needed win for UK's embattled Theresa May

Few people will be more relieved at Friday's long-sought U.K.-EU deal on Brexit than British Prime Minister Theresa May.

Her pre-dawn dash to Brussels to announce the agreement alongside European Commission President Jean-Claude Juncker showed how much May needed a Brexit breakthrough to strengthen her tenuous grip on power at home.

Anand Menon, director of the U.K. in a Changing Europe think-tank, said the agreement "reinforces her."

"It makes people think 'Yes, she can carry this off,'" he said.

Rumors of May's imminent political demise have swirled from the moment she lost her Conservative Party's parliamentary majority in a June election that she had called in a bid to strengthen her hand in Britain's divorce negotiations with the EU.

Instead, a weakened May had to strike a deal with Northern Ireland's small Democratic Unionist Party to prop up her government. Conservative leadership rivals such as Foreign Secretary Boris Johnson circled, holding back from a challenge largely because polls suggested the opposition Labour Party would win any new election.

May is both the pilot of Britain's journey out of the EU and its prisoner. Before the June 2016 Brexit referendum, she had argued for staying in the bloc. But when she won the Conservative leadership the next month, she promised to respect voters' decision to take the country out of the EU.

Her ability to steer the negotiations is limited by the competing demands of pro-Brexit and pro-EU forces within her party and her government.

She is caught between Brexiteers, including Johnson, who want a definitive split with the EU with little compromise, and others including Treasury chief Philip Hammond who want a compromise "soft Brexit" to ensure as little economic upheaval as possible.

Keeping either side from open rebellion is a delicate task, and she has not always succeeded.

Johnson has repeatedly ignored Cabinet rules that say the government should speak as one, publishing his own distinct Brexit proposals and making dismissive comments about the EU.

May has been powerless to fire him, lest it drive him to a leadership challenge.

On Monday May faced further trouble when the DUP, her Northern Irish ally, quashed an agreement with the EU on the Irish border at the last minute. The fact that a party with just 10 seats in Britain's Parliament could derail the entire Brexit deal underscored the fragility of May's position.

Friday's agreement, secured after days of frantic diplomacy, should buy the prime minister some breathing room. It lets Brexit talks move on from the initial divorce terms to the crucial subject of Britain's future relations with the bloc.

Although hardline euroskeptics such as UKIP's Nigel Farage called the agreement a "humiliation" for Britain, high-profile Conservative Brexit supporters backed her.

Pro-Brexit Conservative lawmaker Theresa Villiers said it was "something I could certainly live with."

"All credit to the prime minister, who faced a monumental challenge," said former Treasury chief Norman Lamont.

But there is still no agreement within the British government of what eventual relationship the U.K. is seeking with the EU. And bookmakers still offer shorter odds on Britain holding an election in 2018 than on May's government getting to the end of its term in 2022.

Menon said May "has squared some difficult circles. But the hardest circles remain to be squared."