Boris Johnson, former British foreign secretary. (Chris Ratcliffe/Bloomberg)

Former foreign secretary Boris Johnson continued to attack Britain's Brexit deal in an opinion article Sunday, saying Prime Minister Theresa May had strapped a “suicide vest” to the United Kingdom's constitution and “handed the detonator” to Brussels.

"Why are they bullying us? How can they get away with it? It is one of the mysteries of the current Brexit negotiations that the UK is so utterly feeble,” he wrote. “We have a massive economy; the sixth largest in the world. We ought to be able to do that giant and generous free trade deal the Prime Minister originally spoke of. And yet it’s, ‘yes sir, no sir, three bags full sir’. At every stage in the talks so far, Brussels gets what Brussels wants. We have agreed to the EU’s timetable; we have agreed to hand over £39 billion, for nothing in return.”

It was Johnson's second attack on May in less than a week. Last Monday, he wrote that the negotiated deal is a “victory” for the European Union, headquartered in Brussels, and that Britain is getting “diddly squat.”

In response, May's spokesman said she would not give the piece “any further oxygen” by commenting.

Johnson’s colorful critique echoes the sentiment — if not the language — of anti-Europe members of Parliament who are urging May’s government to “chuck Chequers” and start again.

"Chequers” refers to the Brexit plan proposed by May in July. Under its terms, Britain would maintain its ability to trade freely with the European Union. In exchange, the country would abide by most E.U. regulations. The deal would also allow Northern Ireland to remain in a “customs union” with the bloc if the E.U. drops its push for a hard border between Ireland and Northern Ireland.

Johnson resigned in response, saying at the time that the deal would make Britain a “vassal state.”

Johnson's comments drew a feisty response from his political opponents. Foreign Office Minister Alan Duncan called his piece “one of the most disgusting moments in modern British politics.” It should be “the political end of Boris Johnson,” Duncan wrote on Twitter.

Conservative lawmaker Tom Tugendhat said he was offended by Johnson's use of the term “suicide vest.” Tugendhat survived a suicide bombing outside his office in Afghanistan, he wrote on Twitter. “Comparing the PM to that isn’t funny,” he said. “Grow up.”

May's current foreign secretary, Jeremy Hunt, took a more measured approach. In an editorial alongside Johnson's, Hunt said May is “better than anyone I know at holding the line in the face of intense pressure. But as a country we can help, too, because her efforts to achieve the best outcome for Britain will be greatly strengthened if we are united behind her.”

"I know this Prime Minister and she would never recommend a deal inconsistent with what the country voted for,” he wrote.

British politics watchers have suggested Johnson might be positioning himself as a candidate for prime minister. If negotiations do not improve, May will probably soon face a political challenge.