Representative Tim Ryan said the Democratic brand is "toxic".
It appears that the DNC is the epicenter of that toxic cloud.

In July 2017, the Democratic National Committee (DNC) experienced their worst fundraising month of July since 2007. The organization raised only $3.8 million. For comparison, the Republican National Committee (RNC) racked in $10.2 million. The DNC also added $154,000 to its debt, which now stands at $3.4 million. The RNC has no debt. July wasn’t an isolated bad month for the DNC; it’s proof of a larger, looming problem that the organization faces.
April 2017 was the DNC’s worst fundraising month of April since 2009. May 2017 was even worse; the DNC hadn’t posted fundraising totals so low since in May since 2003. In June 2017, the DNC added $200,000 to their debt and only raised $5.5 million. The RNC raised $13.5 million in the same month. It’s not just wealthy donors that are providing a boost for the RNC; their small donations have significantly out paced the DNC as well. In the first six months of 2017, the RNC received $11 million more in donations under $200 than the DNC did.

The DNC rigged the primaries, refused to even acknowledge it after being caught red-handed, and then refused to consider any serious reforms.
Until this corruption is acknowledged and removed, this will continue to hamstring the Dems.

However, it's not all bad news for the Democrats.

House Democrats' campaign arm raised $30 million in online donations so far this year, breaking their previous online fundraising haul of $20 million.
...News of the record comes after it was reported the DCCC raised twice as much as its Republican counterpart, the National Republican Congressional Committee (NRCC), did in July.
DCCC brought in $6.3 million last month, while the NRCC raised $3.8 million.

It's not just the DCCC. The DSCC is doing well too.

Senate Democrats have already seen strong fundraising numbers — top incumbents are growing their bank accounts, and the DSCC’s raised $28.7 million this year, about $1.7 million more than in the first six months of 2015.

So people are willing to donate to the Democrats, just not the DNC.
How long can this continue before party leaders are forced to do something about it?
After all, this is money we are talking about (or lack of), and that's the one thing that Democratic Party leaders actually do care about.