WASHINGTON, Nov. 4  -- U.S. voters began casting ballots Tuesday in midterm elections which will determine whether the Republicans gain control of the Senate amid growing impatience among Americans with President Barack Obama's economic policies facing high unemployment.

Recent opinion polls for the midterm elections suggest the Republicans are likely to remain control as a majority in the House, while the Democrats are struggling to defend their majority in the Senate.

If the Democrats lose control of the Senate, a major setback of the Party in the midterm elections, it would deal a severe blow to Obama, who would find it difficult to win congressional support for his policies.

A crushing defeat in Congress would also cast a shadow over Obama's political results during the last two years of his second term, analysts say.

The midterm election will make all 435 House seats and 33 of the 100 Senate seats at stake.

In the Senate, the Democrats currently hold 53 seats, and can call on support from two independent members with Democratic affiliation, while 45 seats are occupied by the Republicans.

In the 435-seat House, the Democrats control 200 seats, while the Republicans hold 233. The remaining two seats are independent.

Meanwhile, the rise of the conservative tea party movement, which favors small government, has galvanized opposition to Obama's policies amid the country's economic woes and given momentum to a number of Republican candidates.

The Republicans as well as the tea party supporters have accused the Obama administration of lagged economy recovery, less effort on Ebola, low effect in fight against the Islamic State, as well as his unsmooth healthcare and immigration reforms.

Obama and many Democratic candidates argue that their measures to deal with the domestic issues and foreign affairs are effective and efficient.

In addition, the Democrats take the country's 5.9 percent unemployment rate in the third quarter this year as one of Obama's brilliant achievements in economic development and raising people's living standard although the Republicans say that Obama is still far from his pledge to create jobs and put the economy back on a sustainable growth path.

According to a NBC News/Wall Street Journal survey released Monday, a vast majority of Americans says President Obama needs to change the way he is leading the country.

The survey found 47 percent of Democrats say the president needs to substantially alter how he approaches his job. Two-thirds of the registered voters surveyed say they think Obama should undertake either "a great deal of change" or "quite a bit of change" to his leadership style. Nearly a quarter more respondents called for "just some change," with just 8 percent saying "not that much change" was necessary.

Those numbers compare unfavorably to the weeks before the 2010 midterm elections, when Democrats lost control of the House. While the percentage calling for "quite a bit of change" and "just some change" have remained constant, those advocating for a "great deal of change" has risen 4 percentage points.

A quarter of those surveyed who want Republicans to control Congress say their vote is an explicit protest to the president's job performance - an increase of 10 percentage points from the 2010 midterms.

Still, there are a few signs of encouragement for Democrats. Voters favored Republican control by a 49 percent-43 percent margin in 2010. This year, their advantage is just 46 percent-45 percent.

While voters believe the president needs to shake things up, his approval rating has actually improved in recent weeks. Some 42 percent of voters now favor the president, up 2 percentage points from August and September.