My view is that the terrorist attack will have the greatest electoral impact on the Tory base itself, as heretofore the manifesto had been the source of mixed feelings. Theresa May has still had a mostly uninspiring campaign, however, and the loss of the WFP is a readily quantifiable loss. The upcoming Q&A on the BBC is going to be a very challenging environment for her based on the most recent evidence.
If any politician is considering a strategy which overtly seeks to exploit the Manchester tragedy, i would expect consequences among mainstream public opinion.
Re: current hiatus in campaigning
It was reported earlier today that the Lib Dems expect to resume normal activity on Friday.