She warned of "paralysis in Parliament" if the deal is rejected and said trust in politics would suffer "catastrophic harm" if the UK did not leave the EU.
The PM welcomed new EU assurances over the impact of the deal on Northern Ireland, saying they had "legal force".
The EU said it didn't want to use the "backstop" but, if it did, it would be for "the shortest possible period".
The "backstop" is the fallback plan to avoid any return to physical Northern Ireland border checks.
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