With new flags on the Parkway, new lights on the boathouses, and new efforts to shelter the homeless, the Democrats who have run Philadelphia for more than half a century have cleaned up the city for the Democratic National Convention.

If only they could clean up themselves.

Given its historic resonance, continuing revival, and convenient location in a politically important state, Philadelphia is a fine place for a convention. The city's chief flaw as a backdrop for the Democrats is, well, the Democrats.

In just the past three years, Philadelphia Democrats have seen a congressman, a state senator, five state representatives, and eight city judges found guilty of corruption. A former city sheriff also faces charges, and our top elections official has come under scrutiny for frequently failing to show up to work or, ironically, vote.

The federal and state investigations that swept through Philadelphia's Traffic Court, whose judges were handpicked by the Democratic machine, was so devastating that Philadelphians voted to abolish the court on the same day they helped give Pennsylvania's delegates to Hillary Clinton. One reported beneficiary of Traffic Court ticket-fixing was the only city Democrat on the state Supreme Court, Seamus McCaffery, who went on to resign amid examination of pornographic emails he distributed to other officials.

McCaffery's was one of a few recent implosions of the state's most prominent Democrats. Former Treasurer Rob McCord, a product of the Philadelphia suburbs, pleaded guilty last year to strong-arming potential donors to his gubernatorial bid. Attorney General Kathleen Kane - who like Clinton has roots in Scranton - is facing trial on charges that she leaked confidential grand jury information. Kane initially came under scrutiny for failing to prosecute state legislators caught taking money from an informant and a traffic judge who pocketed a Tiffany bracelet - all of them Philly Democrats.

The standard political response to these outrages reveals the institutional quality of the city's Democratic corruption. When Rep. Chaka Fattah was convicted of running a criminal organization last month, not a single high-profile Philadelphia Democrat expressed public disapproval or called for his resignation. Former Gov. Ed Rendell had testified on behalf of the former deputy mayor who bribed Fattah; Rep. Bob Brady, the city's Democratic chairman, had recently endorsed the congressman for reelection. The city's overmatched Republicans, meanwhile, have too often been complacent or even complicit.

The DNC host committee's efforts to keep its underwriters under wraps won't help the Democrats argue that this is just a Philadelphia problem. Neither will Clinton's close brush with federal law enforcement over her efforts to hide her State Department emails from the public.

Despite the party's support, Fattah's primary election loss in a district he dominated for decades showed that honesty still matters to voters. So have Clinton's diminished polls since FBI Director James Comey criticized her "extremely careless" handling of her email.

No doubt Democrats would rather avoid the corruption issue this week. Here in Democratic Philadelphia, however, corruption is sadly unavoidable.