Several congressional districts around Philadelphia are shaping up as battlegrounds in the mid-term elections next year.

The often-quoted Cook Political Report just changed its outlook for one of them, the 6th District held by Republican Ryan Costello, from "likely Republican" to "lean Republican," giving the incumbent a more narrow advantage in his re-election battle.

The 6th is one of a ring of districts in the Pennsylvania suburbs that the National Democratic Campaign Committee is targeting next year.

In changing its outlook, the Cook Report cited the fact that Democrats have recruited Chrissy Houlahan, regarded as a strong candidate, who's already raised $432,000 for her campaign.

At the moment Houlahan does have a primary opponent, Bob Dettore of Berwyn.

Democrats are excited about the prospect of taking back the House of Representatives next year, citing President Donald Trump's low approval ratings and the burst of progressive activism following his election. The party would need to capture 24 Republican seats to seize control of the chamber.

Republicans are buoyed by their wins in special elections since the inauguration, and the fact that GOP turnout is historically higher in mid-term elections.

In the 7th District, held by Republican Pat Meehan, six Democrats are lined up to run, including state Sen. Daylin Leach and former congressional candidate Dan Muroff. Other announced candidates include Andrew McGinty, Elizabeth Moro, Paul Perry, and Molly Sheehan.

Franklin & Marshall political analyst Terry Madonna noted that Republicans have won those districts handily in recent years, in part, because they were drawn by Republican legislators.

"These districts were heavily gerrymandered so that some of these suburban districts run out into south central Pennsylvania from their core in the Philadelphia suburbs," Madonna said in an interview.

Hillary Clinton beat Trump in the 6th and 7th Districts, the two in the western suburbs. Trump narrowly won the 8th District, centered on Bucks County.

So far, no Democrat has emerged to take on freshman Republican Brian Fitzpatrick in the 8th.

A lot can change in the 16 months before the 2018 general election, and much will depend on how President Trump is regarded at the time.

But strategists I've spoken to say Democrats have to start lining up their campaigns now if they're going to be in position to catch the wave that might sweep them into office next year.

Republicans say there could be a wave that washes away even more Democratic seats.