Tom Houghton was all set Wednesday night to compete for the Democratic Party's endorsement to run for a state Senate seat in Chester County.

"I had my speech memorized, we had all the committee people lined up, we were ready to go," he said.

Then came the late-breaking news flash that the Pennsylvania Supreme Court had handed down an order invalidating a reapportionment plan for the state's 203 House districts and 50 Senate districts. The court said that district boundaries, for the time being, would go back to what they had been for a decade.

Houghton, 43, a lawyer from West Grove, suddenly no longer lived in the 19th Senatorial District in which he intended to mount a challenge to incumbent Democrat Andrew Dinniman in the April 24 primary.

He was out, and not a vote had been cast. Houghton never even got a chance to deliver his speech at a meeting Wednesday night in West Chester.

Scattered stories such as Houghton's arose around the state after the Supreme Court's surprising 4-3 ruling rejected the new legislative map that the Legislative Reapportionment Commission adopted Dec. 11.

It's the first time that has happened since the state adopted a revised constitution in 1968.

With the expected district boundaries shifting by blocks, or even whole neighborhoods, "people who were going to run can't run, and people who weren't going to run - now they can," said U.S. Rep. Robert Brady, chairman of the Philadelphia Democratic Party.

He used the same terminology that Michael Meehan, the city's Republican leader, used to describe the ruling's impact.

"We're reshuffling."

The Supreme Court ruling had no impact on new congressional district maps for Pennsylvania, which were drawn up separately by the legislature and which haven't been questioned in court.

The state and federal constitutions require electoral districts to be redrawn after every 10-year census to reflect population shifts. All districts must have approximately the same population under the U.S. court's one-man, one-vote rule.

Republicans, because of their majority in both houses, were largely in the driver's seat when the maps were drawn. Democrats complained that some districts were altered - or moved from one county to another - to benefit GOP candidates. (However, some acknowledged they'd have done the same had they been in charge.)

Some areas lost population; others grew. One Senate seat was to be shifted from Allegheny County (the Pittsburgh area) to Monroe County (the Poconos).

A House seat in Northeast Philadelphia was to go to York County.

A new House seat, assembled from several seats, was to be squeezed into booming Chester County.

The state Supreme Court issued its order to stop the changes without explaining its reasons. It said those would be forthcoming in about a week.

But the clock is already ticking in the election process. Thursday was the opening of a three-week period, under the court's order, in which candidates for the April 24 primary may collect voter signatures on their nominating petitions.

Justice Max Baer told media outlets Thursday the old map - drawn after the 2000 census - would remain in effect until the 2014 election. The whole court has yet to say that officially, but the timetable would seem to require it.

At ground level, party leaders and candidates were trying to sort out the complexities of the ruling.

Brady said that Wednesday night, within hours of the court's ruling, he received calls from three would-be candidates seeking his support to run in the Northeast district that was to have disappeared from the city. (That is the seat formerly held by Republican Dennis O'Brien, now on City Council.)

"My phones were buzzing," Brady said.

Meehan, too, suddenly had to find a party candidate for the seat.

"We have a district we didn't have two days ago," he said later in the week. "We have a couple of candidates who lived in [other] districts, and they no longer live in the districts. People are maneuvering, that's all I cay say."

In Delaware County, the local Democratic Party had argued in court that the commission's plan to chop up four boroughs among two or more state House districts was unconstitutional. Democrats cited a provision that municipalities should be kept within a single legislative district unless "absolutely necessary" to meet other requirements, such as population equality.

Because the court has yet to issue an opinion to go with its order, Democrats don't know what the justices will have to say on holding such boroughs together.

For now, though, Swarthmore, Darby Borough, Collingdale, and Yeadon go back to having a single state representative.

Andrew Reilly, the Delaware County GOP chairman, was one of many Republican leaders who said they'd be confused if municipal splits turned out to the basis of the court's ruling.

The new reapportionment plan, Reilly said, "contained less splits than other plans that passed constitutional muster" in past decades.

The complexities of the sudden changes were especially felt in Chester County.

As the county has grown in population, more and more Democrats have moved into a region once overwhelmingly Republican. Dinniman, in 2006, became the first Democrat in more than a century to be elected to a Senate seat from the county.

Republicans had an idea how to stem potential further encroachment by Democrats. They planned to strip three House districts along the Route 30 corridor of some Democratic precincts.

Those were to be dumped into a newly created district in the Downingtown area. That district would likely end up with a Democratic House member, they realized, but that was the price of keeping the other districts in the GOP fold.

Those changes were in the plan approved by the reapportionment commission.

Michele Vaughn, the county Democratic chairwoman, said several would-be candidates were lined up to run for the primary nomination in the new district.

"Now this district has vanished," she said.

Contact staff writer Tom Infield at 610-313-8205 or tinfield@phillynews.com.