Democrats need to wake up and understand the stakes involved in holding on to control of the U.S. Senate in November congressional elections, President Barack Obama told Democratic Party donors at a fundraiser Tuesday.

"Something about midterms - I don't know what it is about us. We get a little sleepy. We get a little distracted. We don't turn out the vote. We don't fund campaigns as passionately," Obama said. "That has to change and it's got to change right here, because too much is at stake for us to let this opportunity slip by," he continued. Obama was speaking to a group of more than 40 donors who paid $10,000-$32,400 a ticket to attend a Democratic Senatorial Campaign Committee event at the home of former Senator Chuck Robb and his wife, Lynda Bird Johnson Robb. It was one of 30 fundraisers the president plans to headline through June. He will attend two more on Wednesday in Boston.

Obama said he plans on devoting time and energy to working for Democratic candidates, because advancing issues ranging from the environment to women's health issues depend on keeping control of the Senate. "What I want to do is just emphasize the degree to which everything you all care about -- advancing every issue that is of deep concern to you -- depends on us successfully maintaining a Democratically controlled Senate," he said. "You better hope Democrats stay in the Senate."

A third of the 100-member Senate is up for grabs in November elections as well as all 435 seats in the Republican-controlled House of Representatives. Republicans believe they have a good chance to pick up the six seats they need to take control of the Senate based on public dissatisfaction with Obama. Democrats are in a tight spot, forced to defend 21 seats to only 14 for Republicans. These concerns prompted the White House this year to promote populist measures such as raising the minimum wage, extending unemployment insurance benefits, and investing in preschool programs.

In 2010 midterms, Republicans took control of the House after what Obama called a "shellacking" from voters frustrated with the economy. "We paid a dear price for not paying enough attention," Obama told donors on Tuesday, recalling those 2010 losses.