Democrats lead Republicans in national polling ahead of Tuesday's United States midterm elections, with new surveys showing the party gaining ground in several closely contested Senate races as voters express dissatisfaction with President Donald Trump's handling of the economy. With all 435 House of Representatives seats and 35 Senate seats on the ballot, the elections will determine whether Republicans retain control of Congress for the remaining two years of Trump's second term. A RealClearPolling average of surveys conducted through October 30 shows Democrats leading Republicans 52% to 43.1% on the generic congressional ballot, an 8.9-percentage-point advantage. An NBC News survey conducted October 28-30 found Democrats ahead 52% to 45%, while an Emerson College poll conducted October 24-26 put the gap at 10 points. The generic ballot measures nationwide preferences for congressional candidates rather than support in individual districts, meaning a national lead does not necessarily translate into a corresponding number of House seats. House: Democrats lead nationally Republicans currently control the House, where 218 seats are needed for a majority. The nonpartisan Cook Political Report's latest ratings, updated Friday, place 222 districts in categories favoring Democrats and 195 favouring Republicans, with another 18 classified as toss-ups. Of the 18 toss-up districts, 14 are currently held by Republicans and four by Democrats. Cook shifted another 12 House races toward Democrats on October 30, including Republican-held districts in Colorado and Pennsylvania, reflecting changes in its assessment of the electoral landscape. Read: Michigan Senate race a test of attacks on Muslim candidate, progressive agenda Among the closely watched contests are California's 22nd District, where Republican Representative David Valadao faces Democrat Randy Villegas; New York's 17th, where Republican Representative Mike Lawler faces Democrat Cait Conley; and Texas' 15th, where Republican Representative Monica De La Cruz faces Democrat Bobby Pulido. Republicans are also contesting Democratic-held seats in Florida, North Carolina and Texas, where redistricting has altered the electoral landscape. However, district-level polling remains uneven, and the national figures offer only a broad indication of the environment in which individual races are being fought. Senate: Democrats gain ground in battlegrounds The battle for the Senate is more complicated. Republicans hold 53 seats, compared with 47 held by Democrats and two independents who caucus with them. Democrats need a net gain of four seats to secure a majority. A 50-50 split would leave Republicans in control because Vice President JD Vance can cast tie-breaking votes. The latest New York Times/Siena University polls, conducted from October 23-November 1, show Democratic candidates ahead in six of seven key Senate battlegrounds and effectively tied with Republicans in the seventh. Five of those Democratic leads are in Republican-held states, including Texas and Kansas, which have not elected Democratic senators since 1988 and 1932, respectively. In Michigan, the only Democratic-held seat among the seven surveyed, Abdul El-Sayed leads Republican Mike Rogers 53% to 42%, an 11-point advantage. In Texas, Democrat James Talarico leads Republican Ken Paxton 50% to 43%, while in Maine, Democratic challenger Troy Jackson has 51% support against Republican Senator Susan Collins' 45%. Former Democratic Senator Sherrod Brown leads Republican Senator Jon Husted 49% to 44% in Ohio, while Democrat Adam Hamilton leads Republican incumbent Roger Marshall by the same margin in Kansas. The contests are tighter in Alaska and Iowa. In Alaska, Democrat Mary Peltola leads Republican incumbent Dan Sullivan 48% to 46%, while Iowa Democrat Josh Turek is effectively tied with Republican Ashley Hinson, 48% to 47%. The surveys show Democrats improving their position since September in six of the seven states. Read More: Trump rallies Republicans for midterms Maine shifted from a three-point Republican lead in September to a six-point Democratic advantage, while Michigan's Democratic lead widened from five to 11 points. Kansas moved from a tie to a five-point Democratic lead, while Alaska was the only state where Democrats lost ground, with their advantage narrowing from seven points to approximately one point. The surveys did not include North Carolina, another Republican-held seat where recent polling has consistently shown Democrat Roy Cooper leading Republican Michael Whatley. The latest findings are not uniform across pollsters, and several battleground contests remain close in broader polling averages. Trump's approval and voter priorities The New York Times/Siena surveys found that just 38% of likely voters across the seven battleground states approved of Trump's job performance. Democratic candidates also led among independent voters in every state surveyed, while respondents expressed greater trust in Democrats on the cost of living, foreign wars and protecting the interests of ordinary people. Across the seven states, Democratic candidates held a nine-point advantage over Republicans on handling the cost of living. The findings are consistent with broader national dissatisfaction. An Associated Press-NORC survey conducted on October 8-12 found that 36% of voters approved of Trump's job performance, while 64% disapproved. Also Read: Power bills and data centers cast rare spotlight on utilities in US midterms The economy and cost of living emerged as the leading election concerns, cited as important voting issues by 85% and 84% of respondents, respectively. Health care followed at 69%, while 64% identified the war with Iran as an important issue. The survey also found that 47% of voters wanted Democrats to control the House, compared with 38% who preferred Republicans. For the Senate, the figures were 46% and 38%, respectively. What the polls cannot predict Despite Democrats' polling advantage, uncertainties surrounding turnout and survey accuracy could affect the results. The New York Times/Siena polls, which surveyed between 610 and 1,215 likely voters in each state, had margins of sampling error ranging from 3.3 to 4.8 percentage points. They also found that voters who made their decisions during the preceding month favoured Republicans by nine points, indicating that late shifts in support could matter. Polling errors can arise from inaccurate turnout assumptions, difficulties reaching certain demographic groups and systematic biases shared by multiple surveys. The surveys also found that Democrats' support among some key demographic groups had strengthened since September, although polling has historically struggled to accurately measure white working-class voters. With several Senate contests separated by only a few percentage points, small differences between polling estimates and actual voting patterns could change the balance of power in Congress.