Story highlights CNN's poll of polls finds Clinton topping her Democratic rival Bernie Sanders 52% to 43%

On the GOP side, Donald Trump holds a 12-point lead over Texas Sen. Ted Cruz, 43% to 31%

Washington (CNN) Hillary Clinton and Donald Trump hold leads in nationwide polls alongside their leads in the delegate count, according to a new CNN Poll of polls, with the primary and caucus season now past its halfway point.

The survey average finds Clinton topping her Democratic rival, Vermont Sen. Bernie Sanders, 52% to 43% across six polls released in the last few days, while Trump holds a 12-point lead over Texas Sen. Ted Cruz, 43% to 31%, with Ohio Gov. John Kasich well behind at 19%.

The average suggests Clinton has expanded her lead since mid-February, when an average of national polls conducted after the New Hampshire primary found Clinton just 6 percentage points ahead of Sanders. Trump's lead over Cruz is about the same as his lead in mid-February, but both candidates have grown their share of the vote as the field has shrunk. That poll of polls found Trump at 34% and Cruz at 21% in a field of six candidates.

The new average incorporates results from six national polls conducted by telephone using live interviewers. All were conducted after the delegate-heavy March 15 primaries in Florida, Illinois, Missouri, North Carolina and Ohio. Primaries and caucuses conducted through that date awarded more than half of the delegates set to be allocated via primaries or caucuses.

Democrats are set to hold caucuses this Saturday in Washington, Hawaii and Alaska. Both parties will vote in Wisconsin's primaries April 5.

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