Britain’s Parliament will vote again Tuesday on Prime Minister Theresa May’s proposed Brexit deal. Conservative Brexiteer MPs should swallow hard and support the imperfect deal rather than risk losing Brexit entirely.

They have opposed the deal so far with good reason. It does not provide for a final trading relationship with the European Union, leaving the United Kingdom tied indefinitely to current E.U. rules. This creates uncertainty for businesses trading with E.U. countries and makes it difficult for Britain to sign new comprehensive trade deals with other nations, such as the United States.

The deal’s most controversial element is the so-called backstop. This was included to ensure that the border between Ireland and Northern Ireland would remain free of large-scale customs checks and border posts, something the deal’s negotiators believe to be crucial to maintaining the 1998 Good Friday Agreement that brought peace to Northern Ireland. If a U.K.-E.U. trade deal is not reached by December 2020, the backstop would create different trading rules for Northern Ireland and the rest of the U.K. while keeping both closely aligned with E.U. regulations. This upsets Brexiteers by keeping Britain aligned economically with the E.U. while also angering Northern Ireland’s Democratic Unionist Party, which fears the separate treatment is a first step to reuniting Northern Ireland with the Republic of Ireland.

In a perfect world, Brexiteer MPs would hold out for a better deal. Yet this is far from a perfect world, and Britain’s Parliament is very imperfect. If the deal is again voted down, it is highly likely that Parliament would reject the “no deal” position favored by Brexiteers the following day. In that case, May has promised a vote on Thursday to extend the date on which Britain would leave the E.U., which raises the prospect that a new government might choose to revoke the withdrawal entirely.

The deal does give Brexiteers some important elements of what they want. Britain would regain control over its borders for immigration purposes, meaning it could limit the number of Eastern Europeans coming to the country in search of work. Public anger over the high level of this migration — and the belief that it has cost less-skilled Britons jobs and higher wages — is a significant reason Brexit passed in the first place. Throwing this important gain away in hopes of more free-trade agreements breaks faith with many of the people who voted to leave.

The deal also ends Britain’s annual nearly 9-billion-pound (almost $12 billion) payment to the E.U. after 2020. That money can be used to cut taxes, strengthen Britain’s defense or shore up its National Health Service.

Brexiteers should use their leverage to require May to step down within two months after Brexit takes effect on March 29 in exchange for their support. Conservatives already attempted to remove May as leader of the party in December, and party rules prevent them from trying again for another year. But Brexiteers rightly do not trust her ability to negotiate a favorable final trade deal with the E.U., and May knows that if she fails to get her deal approved, Parliament could trigger a new general election or even supplant her with a cross-party “Remain” alliance that depends on the votes of Jeremy Corbyn’s Labour Party. Saving face and then making way could be in the interest of May and the Brexiteers.

Such an outcome could then result in a new Tory leader who could do what May never did: Prepare and make the case for a “no deal” Brexit. That is the Brexiteer dream, as it would place E.U. trading relations on World Trade Organization rules while giving the U.K. a completely free hand in making new trade deals on its own. The problem with Northern Ireland would still remain; however, signaling that the territorial unity of the U.K. is not negotiable is likelier to produce an acceptable alternative than the current approach.

Britain’s economy is currently so tied to the E.U.’s that this prospect has frightened many Britons, including many who voted Leave in the referendum. Without a strong government providing reassurance and planning for such an event, people have treated it as the equivalent of sailing into uncharted waters with sea monsters circling the ship. Brexiteers cannot get what they want until that fear is calmed, and they cannot calm that fear unless they have control of the Conservative Party and the government.

Failure to take her deal on Tuesday means all their hopes will rest on the prime minister’s character. When there finally is no more time to run out, will she turn to Parliament and her rebellious colleagues and demand them to “back her or sack her”? Will she go back on her promise to hold a vote on delaying Brexit and force a vote of no confidence with the expectation that she could lose, raising the prospect of giving Corbyn power (even if he did not immediately become prime minister)? She could surprise, showing Churchillian courage in the face of immense internal pressure. But most observers doubt it.

Brexiteers should not take that chance. They should take the bird in hand rather than dream they can get two out of an already burning bush.

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