|Corbyn in 2015 - Getty Images|
This isn't to say that Corbyn would be a better choice than May. Personally I do think she will be a stronger leader and terrorist attacks are difficult to prevent even with a large surveillance apparatus. Despite this, one cannot ignore that the bombing has weakened her party.
The worst sign came from a YouGov poll for The Times. It showed that the Conservative Party's lead narrowed to a margin of only 5 percent. May's party has 43 percent and Corbyn's has 38 percent. It's worth acknowledging that this is the worst poll from the perspective of the Conservatives. A poll by SurveyMonkey shows them leading Labour by 8 percent (44-36) and ICM's poll shows them leading by 14 percent (46-32). YouGov was also notoriously inaccurate during the 2015 election. Their last poll before voting indicated a 34-34 tie. The Conservatives won the election by a margin of 6.5 percent.
Nevertheless, I think Labour has some momentum. In addition to Manchester, their rise in the polls is a result of the Conservative Party's election promises, some of which are ridiculous and have been criticized by party members. Some call May a "red Tory" because she departs from Margaret Thatcher's ideology in several ways. Her party has had to backtrack on a manifesto pledge to have the elderly contribute more to their social care. It is being called a "dementia tax" by her opponents.
Then there's a bunch of odd topics that she keeps getting herself into. Animal killings were once tradition in the United Kingdom. The aristocrats of British society loved to hunt foxes, but today the sport is very unpopular. For whatever reason, May thought it would be a good idea to bring the topic back again in support of the hunts.
Right now May has been damaging herself while Corbyn has pushed national security attacks on her. In addition to his promise for 10,000 new police, the Labour leader now says that he will hire 1,000 spies to help combat terrorism. However, May can fight back just as strongly. The Labour leader blamed British military intervention for the Manchester attack. To say there's some kind of parallel between Britain and ISIS shows why he should not be prime minister. Whereas British foreign policy is conducted in the national interest, Islamist extremists are motivated by Islamic scripture. An isolationist foreign policy, presumably including nuclear disarmament and a withdrawal from NATO, wouldn't change anything for terrorists who want to see the end of western civilization.
As of now the Conservatives still lead in the polls, some still by double-digits. As with 2015, it is likely that there are "shy Tories" who will rally behind their party at the last minute and give the prime minister a comfortable victory, but there's still reason to be cautious. May can count on a lead at the moment, but these last two weeks won't be smooth sailing for her campaign.