Mr Johnson’s Withdrawal Agreement Bill has so far sailed through Parliament.
It has already passed eight of the 11 stages needed before it can gain Royal Assent and become law.
But trouble might be just around the corner.
On Monday and Tuesday, the bill will go through the House of Lords report stage – where issues could flare up.
Peers are likely to force votes and inflict possible defeats on the government on contentious issues.
At the Lords report stage, any peer can take part and force votes on an amendment.
Just 10 days before the 31 January deadline, it raises the prospect of the quick progress of Mr Johnson’s deal being stopped in its tracks.
Areas due to come under fresh scrutiny include the government’s decision to rule out any extension of the 11-month transition period to negotiate a trade deal with Brussels.
A vote also looks likely over the removal of an earlier commitment on reuniting child refugees with families in the UK.
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Critics on the Labour and Liberal Democrat benches believe Mr Johnson has ditched pre-election compromises on protections for workers and child refugees after winning a big majority.
Any changes made to the legislation would need to go back to the elected House of Commons, where they would almost certainly be overturned by the Conservative majority.
Before a bill can become law, both the Commons and Lords must agree the exact wording of the bill, raising the prospect of “parliamentary ping-pong” – where a bill is continuously passed back between the houses before they can agree.
However, it remains to be seen how far peers will push their opposition. The government has also warned peers not to frustrate the “will of the people” ahead of the UK leaving the EU.
After the bill has been approved by both houses, British politicians will have no further opportunities to tweak it.