(CNN) Senate Republicans have been trying to thread the needle on health care reform for weeks, but their latest efforts collapsed on Monday when it became clear they couldn't rally the votes to pass the bill.

So why can't they find agreement? Each senator has a different reason to oppose the legislation -- from ideology to re-election concerns to the demographics and health nuances of individual states.

With all Democrats opposed to repealing Obamacare and only 52 members in the chamber's slim majority, Kentucky Sen. Mitch McConnell could afford to lose only two GOP defectors in his quest to push a bill through his chamber. But now four GOP members -- a moderate and three conservatives -- publicly say they oppose the revised plan, and McConnell has moved to trying to repeal now and replace later.

Why is this so hard? Republicans have been promising for years to repeal the law.

When it comes down to the details of repealing the law, it turns out Republicans have a variety of opinions of how it should be done. The members McConnell needs to convince sit on the extremes in some categories of the party and country.

To explain why the Senate's new Obamacare repeal plan is in so much trouble, here are nine charts focused on the 10 Republicans who opposed McConnell's original bill and four of those who had real problems with it.

An analysis from the Urban Institute and Robert Wood Johnson Foundation finds nearly one-in-six nonelderly residents of West Virginia and Kentucky would become uninsured under the original Senate plan, dialing up the heat on Sen. Shelley Moore Capito and Sen. Rand Paul to vote for a bill they can stand behind. Paul lashed out against McConnell's original plan, saying "they're not going to fix the death spiral of Obamacare." A revised Senate plan released isn't likely to change those projections. One-in-eight nonelderly residents in North Dakota, Ohio and Nevada would lose insurance, drawing attention from Sen. John Hoeven, Sen. Rob Portman and Sen. Dean Heller.

More than three in 10 residents of Louisiana are enrolled in Medicaid, drawing attention from Sen. Bill Cassidy. The most recent Senate plan was slated to cut Medicaid spending by 35 percent over the next two decades, according to the non-partisan Congressional Budget Office. Cassidy partnered with South Carolina Sen. Lindsey Graham on Thursday to propose a plan B: keeping some of Obamacare's taxes but giving the money to states to control. Other senators from states over the national average of Medicaid enrollment include Ohio Sen. Rob Portman, Kentucky Sen. Rand Paul, Tennessee Sen. Bob Corker and West Virginia Sen. Shelley Moore Capito, who says the plan "cuts traditional Medicaid too deeply."

Voting for the Senate bill is a particularly hard lift for senators in states that expanded Medicaid under Obamacare. One-in-ten residents in West Virginia are insured through the Medicaid expansion program -- one of the highest rates in the nation. Sen. Rand Paul's Kentucky, Sen. Dean Heller's Nevada and Sen. Rob Portman's Ohio also exceed the national average of 5% of Americans. Alaska, represented by Sen. Lisa Murkowski, has also expanded Medicaid. The bill would dramatically cut funding for Medicaid in future years. State governments elsewhere in the country chose not to expand Medicaid under Obamacare.

West Virginia Sen. Shelley Moore Capito represents the state with the highest proportion of drug overdose deaths in the nation -- 42 per 100,000 deaths -- almost three times the national average, according to the Center for Disease Control and Prevention. She said in late June that the repeal and replace plan "does not do enough to combat the opioid epidemic that is devastating my state." With one of the highest rates in the nation, Ohio Sen. Rob Portman also faces opioid concerns in his state with 30 drug overdose deaths per 100,000. The revised version of the health care bill had added an additional $45 billion for opioid addiction treatment.

The proportion of uninsured Americans has dropped 6 percentage points since 2009, according to data from the US Census Bureau. But the boost nationwide has helped residents represented by Sen. Ted Cruz, Sen. Rand Paul and Sen. Shelley Moore Capito more than most. The uninsured rate in Texas has dropped 9 percentage points since 2009, and the uninsured rate has dropped 8 percentage points -- more than cut in half -- in both Kentucky and West Virginia.

The most real and immediate re-electon threat is to Nevada Sen. Dean Heller. He won his seat by just a single percentage point in 2012, but his state voted for Hillary Clinton by a narrow margin in November. His seat is up for grabs again in just 18 months. Wisconsin Sen. Ron Johnson, on the other hand, was thought to be one of the most vulnerable Senators in the 2016 election, but he prevailed with some help from the top of the ticket. He won't face re-election until 2022, but his seat will likely be in the toss-up category again.

In addition to Nevada Sen. Dean Heller, Texas Sen. Ted Cruz and Tennessee Sen. Bob Corker are both up for re-election in just a year and a half. Cruz has been successful in lobbying for a change to give insurers more flexibility to offer plans that don't comply with some Obamacare regulations. But Heller announced his opposition in an unusual news conference in late June back in Nevada, saying "it's going to be very difficult" for him to support the plan. Arizona Sen. Jeff Flake, who has also been playing the fence on support for the health care plan, also faces the potential for a primary and general election battle during his re-election in 2018.

Ideology marks one of the major hurdles for both the right and the left wings of the GOP caucus. Kentucky Sen. Rand Paul, Texas Sen. Ted Cruz and Utah Sen. Mike Lee -- the three most conservative members -- released a joint statement on the original Senate plan, saying "it does not appear this draft as written will accomplish the most important promise that we made to Americans: to repeal Obamacare and lower their health care costs." Elements of a proposal by Cruz were included in the revised version, drawing his support but possibly further alienating more moderate members. Nebraska Sen. Ben Sasse marks another conservative on the fence. Meanwhile, in the moderate wing of the party, possible defections include Maine Sen. Susan Collins and Alaska Sen. Lisa Murkowski -- both of whom have already united to oppose the nomination of Betsy DeVos and a bill allowing states to block Planned Parenthood funding. Collins has been more vocal in her opposition to the bill so far, saying she needs a "complete overhaul" in order to back the bill. Ratings in the chart above come from DW-NOMINATE, a scoring system developed by political scientists based on Congressional voting records.

While Maine Sen. Susan Collins has enjoyed a re-election margin nearly double the average member of the US Senate, her state narrowly voted for Hillary Clinton in November. And with some pundits wondering if she has her eye on the governor's mansion in 2018, the views of her constituents are also not far from her mind. While Trump won the Buckeye State by a wider-than-expected 8 points, Ohio Sen. Rob Portman still represents a purple state. He's just kicking off his new term and won't face re-election until 2022, but Medicaid expansion and drug crisis are keeping him on the fence.

Graphics by CNN's Joyce Tseng.