Both Democrats and Republicans can draw lessons from the special election last week in Pennsylvania’s 18th Congressional District, located in Pittsburgh’s southern suburbs.

Democrat Conor Lamb leads Republican Rick Saccone by 627 votes. Fewer than 500 military, overseas and provisional ballots remain uncounted, not enough to overcome Lamb’s lead. The only hope for Republicans is a recount that finds errors in Saccone’s favor.

Whatever the outcome, one message for Republicans is that many House seats the party once considered safe are in play in the 2018 election. The 18th was more solidly red than most. It had consistently backed Republicans. President Trump won there by nearly 20 percent.

Opposition to Trump and his policies has unified and energized the Democratic base. Marginal voters who were willing to try a Trump presidency, but are now alarmed by the chaotic nature of his administration, are up for grabs. Women voters are trending to the Democrats in numbers that have to concern the Republican Party.

To stop the political train rushing at them, Republican candidates will need to do more than stoke fears about gun control and tax-and-spend Democrats. They must energize their own base by making the case for the big tax cut bill and crowing about economic growth. And once free of the threat of a primary challenge, many Republican candidates will have to find ways to separate themselves from Trump heading into the general election.

For Democrats the lesson is the importance of picking quality candidates that fit their districts. A progressive gun-control, wealth-redistribution Democrat would have lost to Saccone.

Lamb is a former federal prosecutor and U.S. Marine veteran. His politics are centrist. A gun owner, he backs tough universal background checks, but not bans on semiautomatic weapons or large magazines. He attacked the Republican tax bill on the populist theme of it being geared to the rich and exploding the deficit. A practicing Catholic, he noted his personal opposition to abortion, but recognized legal access to abortion as established law.

In the blue-collar district, he vowed to fight for the protection of union pensions and Social Security benefits. He said health care should be available to all through expanding Medicare.

Knowing the anti-Trump vote would materialize without help, he avoided attacks on the president.

Which party better learns this election’s lessons could well determine the future control of Congress.

The Day editorial board meets with political, business and community leaders to formulate editorial viewpoints. It is composed of President and Publisher Timothy Dwyer, Executive Editor Izaskun E. Larraneta, Owen Poole, copy editor, and Lisa McGinley, retired deputy managing editor. The board operates independently from The Day newsroom.