Both Democrats and Republicans will break out the cavalry this week in a special House election that could have big implications for which party controls Congress after November's midterm elections. Former Vice President Joe Biden heads to Pennsylvania's 18th District, which is in western Pennsylvania, to campaign on the Democratic side. President Donald Trump will go to western Pennsylvania to rally support for the GOP. Texas will also hold its first-in-the-nation primary elections, as Democrats aim for possible gains in the red state.

Pennsylvania election

Joe Biden Getty Images

The March 13 special election pits Republican state Rep. Rick Saccone against Democratic former prosecutor Conor Lamb. In 2016, Trump won the district by 20 points, but polls show a much tighter race for the House seat vacated by Rep. Tim Murphy's resignation. Democrats hope to compete in some red pockets of the country as they try to win control of the House in November, and the Pennsylvania race will partly show whether they can do so. The minority party needs to gain 24 seats to take a majority in the House. Biden, a native of northeast Pennsylvania, heads to the western part of the state Tuesday to campaign for the 33-year-old Lamb. Democrats hope the plain-spoken Biden can appeal to blue-collar voters in the district. The former vice president will speak at a Lamb rally with union members, followed by another public rally with campaign supporters. Meanwhile, Trump will hold a campaign-style rally in the district Saturday night. The president will likely promote the GOP tax plan, as he did during a stop in western Pennsylvania in January, as well as his recent decision to put stiff tariffs on steel and aluminum imports.

President Donald Trump delivers a speech on tax reform after touring Sheffer Corporation in Blue Ash outside Cincinnati, Ohio February 5, 2018. Jonathan Ernst | Reuters

Trump hopes his protectionist move will appeal to voters in the 18th District. His pledges to crack down on trade practices he deems unfair to American workers partly fueled his rise to the presidency in 2016. Trump's tariff decision has highlighted divisions on trade within both the Republican and Democratic parties. Two separate polls for the special election last month showed Saccone with a 6 and 3 percentage point lead, respectively. Lamb raised more than $3.3 million in the first seven weeks of the year, five times what Saccone raised. Saccone has received a major boost from outside organizations linked to House Speaker Paul Ryan and Trump. Outside groups have spent $6.9 million opposing Lamb and $2.4 million supporting Saccone so far, according to the Center for Responsive Politics, while putting only a little over a million toward both supporting Lamb and opposing Saccone. The pro-House GOP Congressional Leadership Fund has largely attacked Lamb by highlighting his opposition to the GOP tax plan and tying him to House Democratic Leader Nancy Pelosi. Its most recent ad shifted issues, criticizing Lamb's stance on immigration.

Texas primaries

Texas holds its primary elections Tuesday. A spike in early voter turnout has heartened Democrats, but it is unclear whether that enthusiasm will hold through November. Texans will pick party standard bearers for 36 congressional districts, one U.S. Senate seat and the governor's office. Republicans hope to stave off disaster: Sen. Ted Cruz, R-Texas, recently told supporters Democrats will "crawl over broken glass" to vote in November.

Sen. Ted Cruz (R-TX) Cameron Costa | CNBC