Trump hasn't really done any fundraising at all, touting his independence from donors and his ability to spend his billions on making sure he makes it to the White House. So his fundraising apparatus is basically nonexistent, leaving him with a little more than $1 million on hand compared to Clinton's war chest of more than $42 million.
Lack of funds wasn't a problem for Trump when he could rely on earned media coverage to propel him to the top of a crowded primary. But the general is a different story; Clinton and super PACs supporting her have outpaced the Trump campaign by millions of advertising dollars in several swing states.
Trump's approach is pretty unprecedented, but if there's one thing Trump's candidacy has taught us, it's that sometimes being unpredictable pays off.