To clarify: we've resolved the linebreak issue on Twitter itself, meaning that if you have a cut-off option, the linebreaks will remain.
It would be sensible to also do this on the website. However, there are many different types of linebreaks you could do. For example turning all the linebreaks into tags would result in this:
"Few battles in history have been more scrutinized than Gettysburg’s
three blood-soaked days in July 1863, the turning point in the Civil"
Notice that the line breaks after Gettysburg's. On this page it would look allright, but I can tell you that it looks ugly on the Twittermail page.
Another option would be to only insert tags when there are two linebreaks, which in your case would nicely paragraph the page. However, I can not speak for other users, so I'm hesitant to put that live.
I will be researching some tweets sent to Twittermail to ascertain whether any solution would result in the most pleasing solution for a large proportion of users. When I have concluded that research I'll be sure to update the Twittermail page.