WASHINGTON, Oct 20 - President Donald Trump’s record-low popularity, voter frustration over the cost of living and a fierce immigration fight are shaping the November 3 midterm elections, which will determine whether Republicans keep control of Congress or Democrats gain the power to challenge his administration.

Republicans hold narrow majorities in the House of Representatives and Senate. Democrats need a net gain of four seats to take control of each chamber.

The outcome will hinge on a relatively small number of competitive races, but the campaigns are being shaped nationally by Trump himself and voter concerns over affordability and immigration. Here is a look at the three issues defining the election:

DONALD TRUMP The president has put himself front and center in the closing stretch of the campaign cycle despite his record-low popularity, with upcoming rallies in Florida, Iowa, Michigan and Texas. Trump's approval rating has fallen to an all-time low 31%, according to a Reuters/Ipsos poll. Yet he has repeatedly urged voters to pretend he's on the ballot, an effort that could motivate Democrats and independents to rally against his party despite the message being aimed at increasing turnout among Trump's base.

Democrats have said Trump has broken his campaign promises to lower costs and end wars. They have vowed to tackle an affordability agenda to reduce Americans' cost of living and hold the administration accountable for alleged corruption if voters give them control of either chamber.

AFFORDABILITY Voters have consistently ranked the cost of living as the top issue this election cycle. Half of registered voters surveyed in a recent Reuters/Ipsos poll cited the cost of living as the most important factor in how they will vote. In the same poll, voters highlighted healthcare, gasoline, food and housing as the top household bills lawmakers should focus on.

Republicans' top legislative achievement was a tax cut extension that slashed roughly $1 trillion in spending for Medicaid, the government health insurance program for low-income Americans, and other health programs. Democrats last year forced a government shutdown over a failed effort to extend expiring health subsidies that benefited 24 million Americans.

Gas prices have spiked since the US and Israel launched military strikes on Iran in February. The national average price of gas is $4.28 — $1.20 higher than it was a year ago, according to AAA. The average cost of diesel is $6.32 — a $2.70 increase from a year earlier.

Grocery costs are up 1.8% over the past year, according to the US Bureau of Labor Statistics data on consumer prices. Federal Housing Finance Agency data show home prices rose 2.1% over the past year. Congress passed a bipartisan housing bill earlier this year. It became law without Trump's signature.

IMMIGRATION Preliminary data from the Department of Homeland Security showed a 95% drop in migrants apprehended at the southwest border compared to former President Joe Biden's administration. The agency said there have been no Border Patrol releases the entire fiscal year for the first time ever.

But fatal encounters with federal immigration agents have occurred in Maine, Minnesota and Texas. The backlash to the death of two US citizens in Minnesota pulled many Democrats in competitive primaries to the left this year, with some candidates calling for the impeachment of then-Homeland Security Secretary Kristi Noem and others saying Immigration and Customs Enforcement should be abolished.

Democrats and Republicans sparred over immigration funding this year in a stalemate that forced Republicans to unilaterally pass a $70 billion bill to fund ICE and the Border Patrol for the remainder of Trump's presidency. Republicans counter Democrats' criticism by saying Democrats support open borders.

Federal immigration officials also raided the Washington home of Democratic US Representative Ilhan Omar of Minnesota this month, drawing widespread condemnation from Democrats. A person familiar with the case against Omar told Reuters one potential aim of the investigation could be to strip her of US citizenship and deport her.

OTHER ISSUES Artificial intelligence and data centers, cryptocurrency, abortion and Israel could also influence voters in individual races. In Ohio's Senate race, for example, Democratic nominee Sherrod Brown has labeled Republican Senator Jon Husted the face of data centers, and the crypto super PAC Defend American Jobs has spent more than $46 million to reelect Husted over Brown, a former US senator who chaired the chamber's Banking Committee.

In Maine's Senate race, Democratic nominee Troy Jackson is hoping voters don't forget that Republican Senator Susan Collins helped confirm Brett Kavanaugh to the Supreme Court, which later overturned the federal right to abortion. Collins is on the election ballot for the first time since the high court made abortion a state issue rather than a federal right.

In Michigan, Republican nominee Mike Rogers has indicated he would accept help from a pro-Israel super PAC that spent more than $30 million backing Democratic US Representative Haley Stevens in her unsuccessful primary against Abdul El-Sayed, who now faces Rogers in the general election. The group has already spent more than $280,000 on mailers against El-Sayed.

Earlier this week, Trump endorsed Israeli Prime Minister Benjamin Netanyahu for reelection.